Kraid: As you admit, you aren't a big fan.
People who aren't big fans of Goldeneye won't get pissed about how sound effect selection for CMag or how pencil-like the KF7 is.
If you're a Mega Man fan, you can raise hell about the slight difference in handling across the six NES games or the alteration to some of the pixels on his helmet.
The 8-bit engine established specific metrics. 16-bit did not only change the number of colors per sprite and add paralax depth, but it changed the metrics. The MMX series on SNES was, like the NES games, in the sweet spot. MM7 was screwy, and they shifted toward the MMX style in 8 and R+F. The later X games were so far off the reservation with 3D silliness that the old fans wouldn't trust Capcom again until they took getting it right seriously. That's why Mega Man 9 was a slam dunk. We want to play Mega Man, not 3D Robot Guy In Blue Armor. The achievements and extras on the side are fine, but the core is what matters.
The nostalgia argument doesn't quite hold up because when someone panders to nostalgia, you often realize the old shit sucked when you are exposed to it again. Watching old sitcoms on DVD will do that to you. But Mega Man is simply a great core design. Not everyone likes it, but those that do like it get a lot of mileage out of it. Super Mario does it right, too, and if you look at the Mario series you can see that they were very careful about only taking small steps away from the formula and falling back when it was a mistake while keeping the good parts.