I wouldn't really consider Mario games "sequels" because most of the time they don't really follow each other stories, its most of small stories or adventures with shared characters.
A lot of Megaman fans attack me for my stance on the franchise, they say i'm not a true lover or whatever, but i don't really like the 2d scroller megaman games but i am a huge fan of the more modern megaman games, like the Battle Network series on the GBA, Megaman Legends on the Playstation and Star Force on the DS.... Sadly they have not continued to produce them and Mighty No.9 was but a Mighty Disappointment :^)
I like 2D Megaman games very much (actually, I only have played X series and Megaman 8 on PS1 as far as 2D goes.)
Megaman Battle Network is my favorite Megaman of all time, it has a simple but powerful gameplay, interesting characters compared to other megaman games, and a good anime series (as far as I watched.)
I wish they made Megaman Legends 3...