Cool, there's now a speedrun of it on youtube
zeroone: I missed your post earlier, so I'll reply now.
The screens are just a big String with different letters for each tile type. This compresses really really well, and with increasing gain the more levels I added.
At first I thought I'd only be able to have 10-15 screens, but at the end I got up to 25 with no trouble at all. I could've made 30 with some effort.
Movement is in 8 pixel chunks, yes. In retrospect, this was a mistake. It came from me just having played (and beaten!) Duke Nukem 1, the old platformer game. It also restricts movement to 8 pixel chunks. I liked the feel so much, I decided to build a game around it. I started out with DN graphics, but quickly realized it might make an even cooler mega man game.
The game is very difficult, yes. Unforgiving, one could say. I like that.