MEGA MAN 4 / Capcom / NES
... especially when Capcom is involved
Ben Franklin once said, "Game sequels are like fishes, more than three and they begin to stink", and he was a truly wise and far-seeing man. Mega Man 4 is the beginning of Mega Man overstaying his welcome on the NES. It adds the chargeable Mega Buster, which is useful when you run into a boss and don't happen to have whatever random weapon is effective against them, but it also makes a lot of the boss weapons that you collect irrelevant (but then, about half of them are totally useless anyway). It also seems to draw its energy from the soundtrack, drowning out about half of the sound channels every time you power it up.
Aside from the general robot lameness, this one also suffers from level design that has largely gone over the border from "creatively diabolic but compelling" to "just plain obnoxious". Of course, Mega Man is also like pizza ... even when bad it's still better than most of the other options, especially on the rather technologically limited NES.
* Gameplay Video