chrisbid said:
well, most of the data on Sonic CD was redbook audio for the game's music. It wouldn't have been that difficult to compress that audio (into mp3 or other format) and making the space required much much smaller. I think it just wouldve taken a lot of extra work, on a disc that was more or less a throwaway in terms of effort. It was cool of Sega to include hi-res versions of the animation movies in Sonic CD though

I agree, the "extras" are what make the Mega Collection so neat - not just the unlockable games, but the movies, comic book covers, full instruction manual scans, and so on. It's a very well thought out archive of data that any Sonic website owner would've been proud of.
My still one and only complain with the entire collection, besides how long it takes to unlock everything with the "open and close" if you don't actually beat every game, is that the emulation in Sonic 3 "freezes" during the third or fourth chaos emerald stage. Thus, no matter how perfectly I'm running, it always throws me off and I make a mistake - so any chance of getting the entire set in 3 is basically impossible.