Ehhh...Megamix has some pretty terrible level design. The pacing in "Green Hill" is all over the place, and "Marble Garden" is a convoluted mess. Those two levels pretty much sum up the design flaws: inconsistent pacing and random nonsensical design.
Marble Garden? You realise it's a Sonic 1 hack right?
Oh right. "Marble Zone." Whatever.
Tweaker had better not be watching this topic right now. He would feel burnt if you were to bash Megamix.