It was already a foregone conclusion that I'll buy this as soon as it comes out, but now that I've seen the gameplay demo I'm actually excited to play it! The trailer was nice an all, but this demo did a much better job of showing the game off. That's to be expected I suppose. I only wish I could properly hear the level music while they were playing it. Hopefully it won't be too long before they release a gameplay video like this with nothing but the in-game audio.
Probably the best info from the demo video is that the game has Not clear on if the Impossible Lair itself is counted in that level total. Depending on how you count the levels and boss/lair levels, that looks like roughly