Megaman, koff~
Megaman is by far my favorite platforming series. I've played and beat all of the classic series (apart from 7) played through most of the X series (didn't they have a few on the PS1? I didn't get that far) Beat Megaman & Bass, Beat Megaman ZX and Advent and tried to get into Zero, but I felt that it was really broken. Comparing the Zero games (I mean come on they call it a 'Megaman' game) to the X games, there really is no comparison. Extending the gameplay by creating little helpers that die (and don't help me much) and leveling up weapons and doing the whole 'I don't care, just do what you want' Metroid-esque feel did not live up to it's successors.
So far my favorite Robot master is DWN-015 (Heatman) from Megaman 2, and so far his stage is as difficult as I remember it. The disappearing and reappearing blocks grow heavily in his stage, causing me to plummet to my death again and again and again; and he's isn't weak to the Metal Blade, so there's that. And he's the only boss I can think of that can actually restore his health using a weapon you launched at him (Crash Bomber). He's also a giant zippo lighter.
I stay away from the 'Grid' series of Megaman, as I have a hard time seeing it as a Megaman title. I think this applies for MML as well for me. I like the Blue Bomber to wear his helmet and jump and shoot. I think the Megaman games are the only games I hate collecting things on (X's hardware does not count as it is required to complete the game). If you have to collect money, coins, bolts, or whatever, you've taken away a key part Megaman. Just jump in, write your password, and jump and shoot. That's it. Going back and forth and back and forth collecting crystals and bolts? That ain't the Megaman way, koffi~
