Watch: A good long look at level gameplay in Cuphead
Cuphead has been an audience favorite at E3 multiple times, which should tell you how long the build-up for this game has been. Long hype cycle aside, you can see from the above video just why it's drawn so many eyeballs: the animation style is so note-perfect and seamless, I'm having a hard time remembering it's all sprites.
Another feature of this video is that it gives us a nice sustained look at Cuphead's level designs, beyond the boss fights that have been featured in the past. You can see that the player here actually struggles with some of the trickier parts of the levels, so you can be assured the developers are interested in making this a pretty challenging platformer. (I do kind of wonder how much of that is due to bad signposting though -- it took me a while to parse the pink spike balls as both damaging and some kind of powerup.)
And it should be obvious given the above, but please remember this is pre-release footage and anything you see here is probably not final and subject to change!