very cool but it's sonic advance a slightly less than perfic imitation of the origonal (the controles in the advance versions are less useful like there is only one speed in the spin dash and you go faster when not in the spin atack)
if you want some cool sonic stuff people found an old sonic 2 beta version with some lost levels on it, only one of them is in any thing that comes close to being playable (most of them are empty haveing only cool sounding names to taunt you, like Genocide City), but it's interesting.
I'll post the ROM (it's beta and nearly unplayable so I doubt it falls under the illigal distribution of abandonware) if anyone wants to take a look at it,
and on the subject, did you know that there is aparently a live and kicking sonic modding comunity, hacking the hell out of the old roms, makeing new levels (ect)