Seriously, this game was a pleasant surprise. I was expecting an inferior version of Sonic the Hedgehog since it's a 1999 handheld game (on Neo Geo Pocket Color). Instead what I got was, I daresay, nearly as good as the original Genesis Sonic games. The gameplay was fantastic, and the levels and enemies were faithful to the series. If the sound and graphics were just slightly better, then I could honestly say it was actually as good as the original Genesis Sonic games.
The game was HIGHLY inspired by Sonic the Hedghog 2 on Sega Genesis. Many of the enemies and a few of the level themes are pulled from Sonic the Hedgehog 2, they use the special stage from Sonic the Hedgehog 2, and the boss battle right before the final battle with Robotnik is against Metal Sonic. But the level layouts are different, you're ARE NOT playing the same game here. And you fight Knuckles, which never happened in Sonic the Hedgehog 2.
My one and only complaint, though, which was a little annoying, was the fact that when you get hit and your rings splash out of Sonic's body, it's trickier to get them back. For a second after you're hit, you simply can't pick up the rings, the game won't let you. And after that second is over, there's a very short period to get a ring before they disappear completely.