Hey guys, I just got finished doing my first overview of the PDF for Ortho. I am, overall, extraordinarily impressed with the work and am rather anxious to see other elements that are missing from the PDF because of the work being continued while the PDF itself wasn't being updated.
I do have some general thoughts and some things that don't quite sit right with me. However, even the greatest works of Shakespeare had their detractors (and they were wrong). So don't think that any of my disagreements should reflect an obstinacy. I'd love to write with you and it'd be silly to expect changes to be made to your overall vision unless you like them.
For the sake of giving an overall impression, I'm going to include the good parts as well though.
Positive Aspects of the Setting
* It's Ortho!: One of the most interesting and alluded to aspects of the Planescape Setting has been brought to existence. Whoever thought of a supplement on this deserves a pat on the back. At last, we can see the fruits of the Harmonium's Dream from there point of view!
* I love the Demon King: It seems like such a perfect enemy for them. I'd love to do some write ups on him if you've got some ideas there. It seems like he's a character that might be in the Abyss but I could also see him from Pandemonium as well. Azlrius just begs for a lot of writing to his goals.
* Love the Lords of Order: They're an excellently realized pantheon and there's just enough hints there's some stuff wrong with them. I don't like the possibility of reconciliation between the Silent Gods and the Lords of Order, I just like the idea that all of the Lords of Chaos have been flat out banished but for the Trickster. It's important to remember the war is WON as far as most berks are concerned on Ortho.
But yes, good, it reminds me of Krynn's pantheon to some extent.
* Love the Government description: While it definitely needs more work and Bureaucracies, which I'd love to contribute too, I think it's overall extremely well realized. The music theme you've developed is wonderful and helps greatly add to the ambiance.
* I'm impressed by most of the Provinces: Again, amazingly good write ups. My favorite has to be Thaera, as the partially conquered Kingdom of Chaos. It seems like some of the best stories could be told about a populous bitterly resisting Harmonium occupation the Last. Dwarvish Armies allied with Humans exterminating Elves and Gnomes as neither side really can reconcile themselves at this point but wondering how it came to this.
* It's recognizably a D&D world: It should and does feel like this is pretty much Greyhawk, Faerun, or Krynn. A generic D&D world that somehow, an adventuring party managed to "win." Bravo.
* An impressive and clearly thought out work: You've managed to cover a lot of elements that are needing to be examined and it's shaping up to be a perfect campaign supplement in a lot of ways. You can definitely tell that the work WILL be finished and it will be impressive when it is.
Negative Elements of the Setting
* Tone down the Genericness in some areas and up it in others: Sometimes, when reading the book, I felt that the "theme" of Ortho was being lost. I.e. that this is a world that has been conquered and the ideals of Lawfulness are EVERYWHERE. It seemed a bit too normal in cases when there should be constant reminders of the uncomfortable nature of their lifestyle.
To me, this book doesn't need more Gulags but the idea that the average Harmonium Clueless on Oerth sees everything through a single lens. You need the stereotypical Ortho citizen to be Jingoistic, religiously intolerant (the LIBERALS on Ortho worship Torm), arrogant, and meticulously troubled the law. With a decided emphasis on those Ortho folk who AREN'T "Ugly-Orthoians", I'd love to do some Ortho psychological write-ups.
I like the idea a lot of Berks in the Harmonium were selected for Sigil because they adapted BETTER than most. 
* No Hobgoblins: Frankly, I'm a little dismayed to find that while Orcs are certainly mentioned as being part of the setting. No attempt was made to incorporate the role of Hobgoblins into Ortho. They seem tailor made for the setting with their extreme militarism, lawful evil alignment, and ruthless attitudes.
With the change of Orcs from LE to CE, as you mentioned in the index, I tend to think that they're a culture that's been drastically changed. You might consider actually making the Orcs of Ortho to be Scro that crash landed and converted the rest.
Either that, or the land is a dictatorship. Overall, I think there should be more hints of other species on Ortho and that its still a generic D&D setting.
* Other Exterminated Species: I wouldn't be surprised if you hinted that other Chaotic Evil Species have been wiped out from Ortho rather than just the Elves and Pixies. Red, White, Green, and Black Dragons all come to mind.
* The Genocide Backpedaling: I think it's a major point of the Harmonium that they were in fact responsible for the massacre. I think that they didn't intend to go out and destroy the Elves and other Chaotic races should be a point, they are meant to be good, but it should also be a case that the chaotic peoples probably resisted to the last.
I don't like the Lich story.
* The Government makes me seriously twitch: Mostly, because the Harmonium Government as described actually seems remarkably MORE liberal and MORE democratic than the majority of Medieval Kingdoms that PCs come from. That to me is a major nono. Also, the Composers that head up the Octave rule as a Council. That, to me, is anti-ethical to the feel of the Harmonium. It should have a single head.
I think it'd be better if Ortho had a Shogun of some sort or a Grand Marshal. It's a peaceful and wonderful world but even in the United States felt it needed a President. The idea that they're a benevolent military dictatorship should be clear. At the very least, it needs an Emperor or Caesar Figure.
* Beholders: You've got a nice Beholder Kingdom here and also did stuff with the Aboleths. For me, I still think that the populous should be way smaller (as someone commented). Frankly, it might do well that the majority of Beholderkind kingdoms are slaves or eager "client" worshipers of the Beholders.
That's clearly not the angle you've gone with though.
* Formians: You should just use them, I think on the Colony World of Eallia.
* Illithids: Do they exist on Ortho?
* Were-Empires: Given that I often associate Werewolves and similar animals with the Wild and Savagery, they seem a rather odd choice to put on the Middle of Ortho. Especially with the issues of infection and some of their "naturally chaotic" natures.
It just seems rather at odds with the Harmonium's ideal. Again, it's like the Beholders in that its just me.
* BIG ISSUE: Needs more ties to Planescape: I know this is Ortho the Prime Material world but it's a supplement for Planescape and I think it's interesting to explore the possibilities of the fact that the Harmonium invaded Sigil, but by proxy, that means a disproportionate amount of attention was focused of the Factions on Ortho.
I think that there shoudn't be THAT much influence but definitely some bits and pieces there. Some suggestions on my end would be...
1. The Burrowdogs are actually founded by the Revolutionary League.
2. The Revolutionary League has stuck Faction "Moles" in with Teleportation devices through the portals (easy with their Faction Ability) and has been bringing other members in.
3. The Mercykillers should have a Fortress on this planet and also the Guvners representatives as well. The Mercykillers are probably mostly now "Son of Mercy folk"
4. You've already hinted there's a ridiculously large number of Slaadikin and Tieflings on the planet. You should maybe also make a note for Aasimarr. I say go extreme. Have Aasimarr practically worshiped by the ignorant sods and Tieflings are creatures burned as monsters when found outside of their homeland.
5. Divine Harmony should also have approved representatives from most other groups (Xaocists and Indeps are never welcome while Sensates should probably be greatly discouraged but they ARE there)
* Don't need to expand the Gods further: I think you just need to note that the standardized D&D gods of Corellon, The Fairy Court, Gruumsh, The Great Mother, and so on are/were worshiped there. No need to actually detail them. Space concerns seems like it's going to be an issue.
I don't think you need a new Goddess of Magic either. Just ascribe that quality to another deity or pair of them in the Lords of Order/Chaos.
* Gods that should be added to the list: I think Marduk, Bahamut, Tyr, Bane, Hextor, and Heironeous should be added to the "Approved God" list. It definitely needs more "Evil but Tyrannical" gods.
* Factol Sarrin shouldn't actually be Leader of the Harmonium: I tend to think that you should break typical viewpoints and that Sarrin is only the head of the Harmonium in Sigil as opposed to the head of the Cage and one of the Ruling Council itself. I actually got the feeling that he's little more than high level but decidedly "Vice President" type figure.
It could still work if he answers directly to the Grand Marshal or whoever, but right now being Factol of the Harmonium in Sigil means he's at the top.
* The Alliance with the Baatezu: I think some explanation is going to be needed for why the populous is a willing group that allies with Devils when most Primers know they're bad news. I tend to think they might have come to help after the Abyssal charge. Nevertheless, I tend to think that the Harmonium is possibly keeping their alliance with the Devils in the Dark if at all possible. Higher ups in everywhere from the Church to the government know and it's a big Elephant in the corner.
* Harmonium Colonies: I would like to note that I'm not sure given the Harmonium multiple worlds is such a good idea since the Manifesto implies Ortho is one, but given the work you've done, I can change my view. I think that Fortitude and it's place in the Harmonious Ascension should be detailed here. The Plane of Arcadia that fell to Mechanus should also be detailed and what's happening to its citziens. It seems like a major war.
Also, Meter seems to be way too allegorically Medieval Europe. R'Talnir confused me. Is this a "lost" Harmonium Colony?
* Needs NPCs: You know that.
* Needs more Government Detail: You know that. I'd like to help here.
* Monsters: Oddly, I tend to think some of these write ups might be better saved for a Planescape MM.
As a sidenote - the reasons the beholders, weres and other colonies are there, and the hobgoblins aren't:
1) Beholders are mentioned as a primary race in canon works, which is pretyt cool.
Their province was one of the first provinces worked on so it was originally developed in something of a vacuum compared to the rest. So it probably needs some revision.
2) Weres - some of the weres are naturally lawful. I also felt it would serve as a good example of how sometimes the Harmonium *does* come up with a reasonable and sane solution to a problem. Instead of killing the marauding savage beasts, who are in many cases essentially cursed victims... find a way to control them and integrate them. Convert instead of kill. A number of races more commonly thought of as 'evil' are brought into the Harmonium is just such a way. After all - if genocide is not a reasonable answer (and given the shame of the past - it's not.) Then the Harmonium *must* find some way to allow such races to live in harmony. The beast-folk are a poster child of this effort. That and viking werewolves just sounded *cool* in my head, like something players would want to play.
3) Other colonies, in canon it's noted that Orthos empire is multi planar. At one point we were thinking of teaming up with Spelljammer.org on a co-release of material.
4) Hobgoblins. Honestly - I sorta forgot about em. Opps? Please accept my apologies? They haven't been used heavily in any of the games I've played in, and you're right - there should be some mention of them. We still have some provinces to work though - perhaps Shrinyko? (Horribly misspelled the name of that one I think.)