Mega Man 6/YMMV

Anticlimax Boss: Even by the game's standards, the Wily Machine is embarrassingly easy to defeat. The fact that every form is weak to the Silver Tomahawk doesn't help.
Badass Decay: Beat, whereas in Mega Man 5 he is a Game-Breaker, he's severely nerfed in this game, and can't even target Bosses anymore.
Game-Breaker: The Jet Adapter utterly breaks whatever difficulty the platforming segments have — Mega Man can fly and hover in it and move quite fast, and it only takes a second for it to recharge and take off again. You only need to take it off during a boss fight or the odd occasion where a charge shot, slide, or your Power Adapter is needed.
It's Easy, So It Sucks: A common complaint about the game is that its difficulty is generally much easier than that of previous entries in the series, due to the Robot Masters' very simplistic attack patterns and the addition of Jet Mega Man.
Scrappy Weapon: The Plant Barrier is considered the worst shield weapon in the Mega Man series. It has the same flaws the Skull Barrier from Mega Man 4 has, but wastes much more energy, making it far more impractical.
The Untwist: You mean to tell me that guy who looks like Dr. Wily with a beard, Lennon Specs, a cloak and a bindi is in fact Dr. Wily in disguise!? The fact that the previous two games had nearly the exact same plot twist didn't help manners either.