Rockman 4 Minus Infinity/YMMV

Best Boss Ever: Pharaoh Man in Pharoah Man's stage because it has two parts: one on the outside and one inside the pyramid. At the end of the first part, he destroys the arena and starts the second part by turning red, getting a health refill and becoming a berserker at the same time. The fight resumes, but you're under the curse of the pyramid.
Breather Boss: Proto Sniper Joe counts as one because Mega Man can bring in an Apache Joe chopper from the previous section and snipe him from a safe spot.
Crazy Awesome. The entire game.
- This video's description (describing Wily Stage 2) says it best:

This is a level where you kill a bunch of enemies on conveyer belts and then get sucked into a Gradius level. Then Dr. Wily makes a dark clone of you that stands on the ceiling and takes four of your weapons with the patented Dr. Wily Stealing System.

But it's Pure Sabe, so it's manageable.

That One Boss: Toad Man and Dust Man have taken a level in badass.
- Toad Man's movements are now erratic and rapid. He'll jump if you try to shoot him or get close to him. Watch out if he hits you with his rain attack.
- Dust Man can heal himself with your attacks except Toad Spell when he sucks in his debris. If he sucks you up, he turns you into an E-Tank. Mash the buttons quickly or he will give you a One-Hit Kill by booting you into the incinerator.
The doctor himself has also tooken a level in badass. Instead of appearing for breif amounts of time while firing a managable amount of projectiles, this Wily Capsule fires high-speed lazers a seemingly random areas. Also, he never stops firing when his health gets to a certain threshold.
That One Level: Skull Man's level is made up of various platforms from the Mega Man series over very large Bottomless Pits. Beat can make it little easier.