Mega Man 9 was highly praised, the thing is Mega Man universe has a lot of ramifications, some of them are in the same timeline and some of them are in a different universe, but usually people only care about 2 of them: Mega Man and Mega Man X, Mega Man, as proved by MM9, is a series that works like a charm on 8-bit art (if you look at Mega Man 7 and Mega Man 8 people usually remember those as the black sheeps of the series), and Mega Man X reached its peek with the 16 and 32-bit 2D games, when the 3D games on the PS2 came (X7 and X8) people fell out of love...
It comes down to preferences, that's why Mega Man 9 was planned as a retro 8-bit game, and i can say for sure that if they make other Mega Man X games those are gonna be 2D...
The other series like Zero, ZX, Legends, Battle Network, Star Force, etc. have usually a small audience...
Of course, there are fans (like me) that follow the all the series almost blindly (and i say almost because despite being my favorite series ever i know which games are just bad)...







