These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anti-Climax Boss: Shadow Man in the first Cossack stage. Your last non-Bonus Boss fight with him is also the easiest; you can easily rapid-fire him with your buster and he'll die in a few shots.
Awesome Moments: Mega Man using Rush Cannon on Wily's saucer in the best ending (or ramming him with Hell Wheel in the normal one).
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.
You get to fight Terra, and you get to use his weapon!
Averted in The Mechanical Arena, as you cannot bring in an Apache Joe chopper or the Spark Chaser for each respective battle, forcing you to rely on your default weapons.
Complacent Gaming Syndrome: The constant use of Hell Wheel is guaranteed. The fact that you use it in the final chase of the game doesn't help. Interestingly, the Hell Wheel was far more broken in early builds of the game than in the current release, able to one-shot most enemies. While it isn't a Game Breaker anymore (using it in the wrong places is a good way to drain your health), it remains the go-to weapon for Speed Runners.
Ending Fatigue: No fewer than three "final bosses", and that still isn't the end of the game.
Dive Man is weak against Spark Manbow, because the ocean depths are very dark and thus any light entering Dive Man's eyes damages him tremendously.
Skull Man is weak against Recycle Inhaler because his materials are easily recyclable.
Pharaoh Man is weak against Drill Torpedo because drills dig through excavation sites.
Toad Man is weak against Pharaoh Shotgun because the move uses the power of the sun to kill things. Toads can't stand the heat.
Bright Man is weak against Spark Manbow because it causes a massive power overload.
Wave Man is weak against Hell Wheel because it is a contact-based move like Charge Kick.
While Shadow Man's multiple appearances could be chalked up to Author Appeal, there is a reason for it. In the official materials, Shadow Man is described as Wily's bodyguard/right-hand man. It would make sense if Shadow Man himself does the field job. One encounter even has him maintaining Pharaoh Man's level.
In the credits, Wily Stage 2 has the subtitle "Rushed-Out Products". That would explain why all the enemies are colored gray during the first half of the stage (where Mega Man gets rushed by just about every kind of minor enemy from the game): They were rushed out and had no time to be painted a different color.
Wily escapes even in the best ending, using one of the enemies to carry him off... But it drops him, and then picks him up again. Mega Man sighs.
The final boss fight. After Mega Man disables the alien hologram, Dr. Wily hastily modifies the projector and tosses it at Mega Man, which makes him lose all his weapons and creates the Petit Robot Masters, who themselves are humorous in their manner of attacking all at once.
In the normal ending, Wily begs for mercy at Mega Man like usual. In the best ending, however, Wily ends up begging for mercy at Rush.
Game Breaker: Almost every single weapon is a game breaker in a certain situation.
Holdable Control Ring Boomerang slaughters stationary minibosses, and if you have the pertinence it can even take down the Boss in Mook Clothing Jumbig within a couple of seconds.
Hell Wheel allows you to speed through the stages and in earlier versions, it could kill almost every enemy. Use this in Wily Stage 2 and the whole first half (Except for the Jumbigs) is an entire joke. Many people doing playthroughs tend to use this ability.
Recycle Inhaler can destroy almost every enemy in one hit and it makes powerful items. In raocow's words, it'll DUST THEM UP!
Rush Cannon and Wishing Star allow you to defeat anything in one hit. Except for major bosses of course.
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.
Shadow Man's final appearance has him move 'very fast and flood the screen with projectiles. As qzecwx put it:
"Well damn. Puresabe put out all the stops here. 112 HP, no true weakness, invulnerability nullification everywhere, OHKOs, weapon energy drain, twenty-odd different attacks...!"
That One Level: Skull Man's level is made up of various platforms from the Mega Man classic series over very large Bottomless Pits. Beat can make it a little easier.
The curses at Pharaoh Man's stage can be a pain the ass, especially the Roulette Curse.
Wily Stage 2 ... with two Jumbigs.
Wily Stage 4 is not a cakewalk like it was in the original Mega Man 4. First, you have to fight three Chimerabots which are hybrids of some of the most annoying boss combinations possible (Cut Man with Elec Man's speed and attack pattern, Wood Man with Quick Man's spastic speed and less frailty, and Needle Man with Gemini Man's cloning ability). If you don't die at all from the first two, or during the entire game for that matter, you fight Shadow Man instead of Gemini/Needle instead, who is possibly the hardest boss in the entire game with a huge array of attack patterns and instant death attacks, but does give you a powerful reward. After beating the third Chimerabot or Shadow Man, you fight Wily Capsule. Final boss, right? NO. You then go through a creepy underworld-like level with bubbly enemies that are hard to kill with any weapon. Getting around is also hard without dying. Fortunately, the true final boss in the game right now isn't hard, thanks to the Eleventh Hour Super Power Proto Man eventually gives you. After defeating that final boss, you then go through an Escape Sequence segment where you have a limited amount of time to escape the exploding Wily Castle using Hell Wheel. Then after that, you're finally done.