Keeping the Commander Keen comparison, Commander Keen 2 and Mega Man 2 were both better than their respective forerunners for different reasons. Keen 2 offered more of what the first game did, while Mega Man 2 added rock, paper, scissors to boss fights and steered toward easy instead of hard. Both series had a disappointing third title, and both third titles failed for the same reason: the games were too hard. Mega Man 3 also lost rock, paper, scissors boss fights, with arbitrary weapons working against select bosses.
We still have a decent game however. “Proto Man,” a mini-boss and a new nemesis for Mega Man. Mega Man now has a dog, Rush, who helps him with high jumps and flying. These characters add some personality to the game. I was reading about certain MM3 bosses appearing in the animated series, and the comic books too; unfortunately, Keen doesn’t have this much backstory. The Mega Man Legacy Collection has a lot of promotional imagery as well as backstory, which is a nice touch. The actual stages are challenging, just as they are in the first game. Now however, there is a set path that saves you from damage, so you can’t blame poor level design when you falter. Mega Man 3 aims to increase challenge and boss frequency, and succeeds, but we lost the accessibility in the second title, or even the later Mega Man X.