I'm going to chime in and agree with jarosh and segata, but that's a given because they understand how bad MM4 is. I haven't been playing it that much, and I'm one achievement away from platinum, and it's honestly not going to be that hard to get it on easy. Wily is a joke, as are his stages. The difficulty is really poor, but even worse, the gameplay is totally unimaginative. I loooooved 9. It was my favorite after 3 and I liked it even more than 2. Mega man 10 just seems like they had about half of a good game planned out and then did the rest in two weeks.
-Mid bosses suck, especially wily castle boss 2 (shoot a crab in the face for 3 minutes man).
+New devil machine is good, clever use of space.
+Sheep man's weapon is novel and useful in certain situations. Put it over a gap to zap those parachute bombs before they can hit you.
+Sheep man's level is fun, both with the disappearing color blocks and the electricity treadmills. It could be tougher though. It's very easy even on hard mode.
-Music mostly sucks, only a few good tracks such as nitro man and pump man's stages.
-Weapons are basically all just projectiles, nitro mans weapon would be cool but there's not really anywhere to use to go up walls thats very useful.
-Stages are really ugly.
+ A ton of content. This really saves the game for me and keeps me from hating it. The challenges are awesome (in that you can practice on bosses in all 3 difficulties), protoman is free, hard and easy mode are included.
It's just very bleh. Not MMZXA horrible, but still a piss poor follow up to 9.