I like the sheer height and dominance of the tower compared to the rest of the city. The flying creature adds to the sense of the tower's size.
I would recommend trying to make the rest of the city look like a city. It is sort of city-ish but it looks more like the bottom of a spike pit than a place where fiends live.
Still, you drew something that's supposed to be enormous on a relatively small canvas, and that says a lot right there 
Thanks. I tried to get it more detailed, but it's something that I need to work on. It don't look right the first time I started the city, so I tried to simplify it. Maybe I took it a bit too far. I was much more focused on conveying the sheer scale of the tower.