I haven't gotten endless attack due to trying to be frugal with my points (I'll probably buy it on december, but it looks fun now that I've seen it on Youtube. And there's even the first section of Wily's first castle mimicked! And probably MANY more.)
However, I did get Proto Man. SJ forgot to mention his jumping shield (I love using this to kill machine gun/uzi joes) and his two-buster-shots-on-screen problem. That one less shot does manage to screw me over on the first Wily boss, though. And the knockback makes the third Wily stage downright hellish.
Also defeated all the 8 main bosses with the proto buster only. This mostly isn't much different, but some boss tactics have some different methods or additions that make things somewhat easier:
Galaxy Man: Slide away from the black hole and use a charge shot when he appears. You don't have to worry about being sucked in if your slide takes you further easily. In fact, unlike the majority of bosses, the charge shot works better here.
Magma Man: Probably the biggest changes. You can defend against Magma Bazooka! I use this to advance and defend when he fires from the second-highest platform while I'm at the second lowest. Also, if he jumps from the lowest to the second lowest, you can slide under him, (AS I PREDICTED back when using Mega Man). But seeing as he kills you in four hits, still not easy.
Plug Man's still insane, and harder when you can only take four hits...
Nontheless, a mode I'll play passively every so often.