I bought one of these shortly after release, but only now got around to playing it. The controllers are more sensitive than I remember the originals being, particularly with regards to the D-pads, but overall they feel pretty good. The game selection is pretty good, apart from lacking Sonic 3 and S&K (guessing they're being held back for a Genesis Mini 2), and I wouldn't have minded a sports-type game of some sort. Overall, though, they seem to have done a good job.
-Adam