My initial reactions:
Sheep Man: This is just bizarre...it reminds me of freeform jazz. It grew on me a lot when I listened to it on the second loop, and I think it's rather clever for an 8-bit song. I'm not fond of the intro (or the boss itself for that matter >_>) but the rest is good.
Commando Man: It definitely fits the stage well. It's like an evil miliarty march mashed up with a standard Megaman tune. The changing time signatures in the last segments are rather cool, as is the percussion.
Nitro Man: Standard Megaman fare, really. It reminds me a lot of the more intense Mega Man 5-6 songs (a good thing, I might add). It lacks the uniqueness of the other two before it, but it makes up for it in Mega Man class.
Strike Man: The second half of this song is pure brilliance, and very unique for a Megaman song. I'm not as fond of the beginning though. It's rather generic, epecially compared to the other songs we've seen so far.
Blade Man: This may be the most complex 8-bit Megaman song ever. Seriously, this is too cool for words. It's going to be hard to beat this one. By the way, I think most of this soundtrack was influenced by prog rock and jazz. Seriously.
Solar Man: Those guitar bends are just awesome, as is the percussion. The warbly sounds at the end are VERY out of character for a Megaman game. In fact, this whole song sounds like something out of a Commodore 64 shooter. Definitely one of the more kickass songs in the game.
Chill Man: I honestly think this theme is rather...out of place for an ice stage. And it's not particularly impressive to begin with. One of the more forgettable themes in the game.
Pump Man: Yet another technically amazing song. The pitch bends in this one are particularly soulful. Also, the warbles at the beginning actually remind me of a pump. That may sound weird, but it's quite true.
(I'm skipping the menu themes because I don't care
)
Wily .5: This is an interesting piece, definitely. The echoes and static are definitely unique. It's short, but sweet.
Wily 1: The hard rock waves at the begining are really cool. The runs that ebgin towards the middle remind me of earlier Megaman tunes (definitely a good thing). I think this works really well for a Wily Stage theme, although it might be too epic for stage 1.
Wily 2: Another rockin' intro. These songs are getting more intense as the game progresses
. Another nice one, though. Reminds me again of earlier Megaman works.
Wily 3: Slows down the pace a bit, but it definitely works. It's not as impressive as Wily 1 and 2, but it's definitely quality music.
Wily 4: I'm running out of things to say. I mean, these are all so awesome
. The crescendoes in this one are really nice, and the ending effect is one nasty son of a banana. The rest is a little bland, though.
Wily 5: Why hello there special effects! You're making quite a splash there in the background! Seriously though, the background thing going on is quite amazing. Capcom is really pushing this to its limits.
Boss: Definitely different from your normal Mega Man boss theme, but in a cool way. It almost sounds like it could pass as a robot master stage.
Mini Boss: Definitely more typical Mega Man boss fare, even though the synths are definitely new. Capcom is really loving these warbles, aren't they?
Wily Machine: More epic final boss fare. It's not what Mega Man 9 did, for sure, but it's definitely a perfectly epic way to end the game.
Wily Capsule: I think I prefer round 1 of the fight to this one. It sounds more epic IMO, and I think the two should be switched. But again, not bad. Another great way to end a strong OST.
My favorites: Sheep Man, Commando Man, Blade Man, Solar Man, Wily 1, Wily 2, Wily 5, Wily Machine