Impressive...Very impressive indeed.
I'd like to say that is the best Megaman-based game I've seen on Newgrounds since Megaman X Next (if you wanna play it, just search the 'portal, lazy arses!). I've also always been a fan of Ikaruga, which I played on my Dreamcast, and while I never went past stage 3, it's still was a great game.
So let's get it straight: good crossover concept, good, non-repetitive missions(the stages were, at least, differents from what I saw), an little push to the player to get better (the cheat codes!), good animation(not very choppy -- if at all, and that might be my computer actualy) and nice play control.
And decently challenging, to boot. All in all, very, very nice game, and it's going on my favorite list.
One nitpick...there is a large hole that you need to jump in the second part of the third stage, and I gave up at about the...fifth time. It's a liiiiittle to big. Unless I'm missing something. Oh well!