Simply put the originals should play either as good or potentially better than the originals (correcting system limitations, especially applicable to the NES). Extra content? It's nice, but it's not mandatory. Controls adjustment? Well, when you're working with a new controller it happens. AC's reversal was senseless but by no means a deal-breaker for me.
MMAC was kind of a mixed bag. 8 was horrid, and there were a few musical hickups in the others (Bass's PF Ending is the most painful). 1-6 are improved over the NES performance (nice to eliminate flickering and sound channel interference), but at the same time, the fact that they based them on the PS1 Complete Works only to strip out the vast majority of the extras annoys me to no end. I actually did like the menu interface, though. Beats the hell out of XC's, and the new BGM for it was awesome. Took the best two title themes in all of gaming history and mixed 'em together, brilliant.
XC achieved more accurate emulation, far superior to AC. At the same time, the fact that they couldn't properly loop SNES music is unbelievable (I can only hope that is a sign of the new soundtracks that were allegedly cancelled; DAMN I WANT TO HEAR SOME REMIXED X2!!!). Other than that it works. X6's lack of voice is disappointing but at the same time I can understand it as a filesize-conscious decision (unlike, say, ZX). Then again, maybe if they could have properly sequenced the SNES it wouldn't have mattered.
Mega Man X Collection is much better, though I'd prefer the original X3 instead of the one with the music that sounds like a broken merry-go-round...
Even if there are several instances where I prefer SNES music, and I most definitely prefer SNES SFX, I'm still happy they brought the PS1/PC version over and very much admire their decision to do go. Why? Because that version was previously unavailable in this region. It was a great act of fanservice. Granted, the option of both would have dodged the issue, but GCN disc limits and (again) lack of proper SNES sound emulation probably didn't help matter.
1) Pixel perfection - In short, when I purchase a collection that contains a number of my favorite games, I would prefer to be able to play those games verbatim to how I remember them. How the Mega Man, Capcom Arcade and Sonic collections have done a lot to fall flat in this area, in spite of the technology that was available even at those times, baffles me. I should not have to deal with any thing relating to graphical glitches, slowdown, and other runtime problems that didn't exist in the original version.
Refresh my memory, what runtime issues did Sonic Mega Collection have? Granted my focus is mainly on S3&K, but the only major issue I noticed is the weirdo instrument swap in Sky Sanctuary.
2) the "All Stars" way - To this day, I don't think any collection of games has done as much as Ninty did with this pack. Take all of the old stuff, give it a fresh coat of next-generation paint, while still possessing a great deal of what made those original games as sexcllent as they always were. That's the other way I like my collections, in that, I would certainly love to see something that gave me perhaps not only that which I was familiar with, but more on top of that. As long as it doesn't take away from the original package deal, then shoot, GIMME!
I love All-Stars, but it is not perfect. There is a valid point in that jumping physics for SMB/Lost Levels are off. Lost Levels also got nerfed in some areas (not as badly as Mario Bros. Deluxe, but still). The NES original is a whole other beast. And then some minis are missing from the SMB3 Versus selection. NES also has the definite superior fireball SFX (I thank NSMB for preserving it).
On the other hand, the fresh coat of paint worked wonders, especially for 2/USA and 3. And the FRIKKIN NEW BOWSER MUSIC IN 1/LOST LEVELS is something I really wish Nintendo would acknowledge in all their retro-loving (that and the fact that bridges over lava shall be destroyed with an *AXE* and not a damn switch).