Mega Man 2 is a great game until you get to the Wily stages. Those levels are pure bullshit.
It doesn't even take long to get bad. There's this awful section in the first Wily stage (stole it from StrategyWiki, which is why that E is there).
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See those ladders? What you're supposed to do is use Item 1 get across the chasm to get to the other one. Item 1 is really finicky to use, and trying to get to the ladder on the left requires precise timing and jumping. Unfortunately, the sequence right after this is the Mecha Dragon, and it's extremely easy to die to it, meaning if you fuck up you're doing the ladder shit again. And if you run out of energy, tough shit. The only way you can get more energy is to go down the ladder and fight those shield bastards, who take forever and deal a lot of damage.
There are other parts that are just as terrible, if not moreso. The aforementioned Mecha Dragon is a cheap bastard and the Boobeam Trap (aka the boss you can only damage with Crash Bomber) is easily the worst part of the game.