I've played all of the games on their respective consoles, and playing it on the GC just isn't that great.
I won't go into all of the games, I'll do those separately since this review is for the collection.
Controls: Most people gripe about the A and B being switched, while this is VERY annoying, and VERY difficult to get used to, I got used to it. What I can't stand is the control stick choice. You either have an analog thumb stick(which isn't good at all for precise platformers like Mega Man) or a very small and uncomfortable D-Pad.
In most copies(though some later ones fixed this) the sound effects in MM1 are played a Pitch higher, which for the most part isn't all that annoying, unless for play it for more than 15-20 minutes. Most of the other NES games are slightly muffled, but this isn't generally a huge problem.
Mega Man 7's sound is absolutely atrocious.
The music MIDI is all mixed up, some sounds/instruments play too long, too short, too loud, too low, and some don't even play at all. Also the controls for MM7 on the GC are especially annoying.
MM8: The second 4 robot master voices are a pitch higher when played in the levels...(as if Aquaman wasn't gay enough)...
Gameplay: This hasn't really changed. It's good ol' Mega Man.
Actually pretty good, I thought the screens and everything were top notch. The extras, though few they are, are good enough.
Only problem is the removal of the ending Scene in MM7, which deeply saddens me. Atomic planet says they couldn't do it, but I think they could have and were just too lazy to do so.
Most of the problems in this version, aren't even present in the PS2/Xbox versions, besides some muffling, the removal of the final scene in MM7, and the problems in MM8. Also, the other versions have remixes unheard in this version(Also, this version has a G4 segment about Mega Man, the PS2 version has the fist episode of the heavily westernized cartoon, and I believe the Xbox version has both). Which is quite curious. The only reason I give this version 7.5, is because it's Mega Man. The actual games are fun, but I think this version of the collection is EXTREMELY sloppy. If you have a PS2 or an Xbox(though I don't know too many who have an original Xbox) get those versions. If you only have Gamecube, and obviously not their original respective systems, get it, if you don't mind it's flaws.
To be fair, maybe I'm too particular, but I think they could've done a MUCH better job.