More fun than the last two.
So what can Sonic do? He's slightly faster than Tails, and he can take advantage of the abilities of the different types of shields. There's the bubble shield, which lets you breathe underwater (Sonic can bounce around with it); the electric shield, which magnetically draws rings to you (Sonic can get a shock-boost in the air from it); and the fire shield, which protects you from flames (Sonic can turn into a fireball and dart through the air with this shield). The shield powers don't really give Sonic an edge over Tails' abilities though.
The fun doesn't end there though. You can also hook this game up to your Sonic & Knuckles cartridge and add Knuckles to the fun. Many will argue that it's easier to play as Knuckles than as Sonic or Tails. Knuckles possesses the ability to glide through the air, cling onto and climb up walls, and ram through walls that Sonic and Tails have to spindash through. (In fact, there are some walls which Sonic and Tails can't break at all, which Knuckles can break with ease, and he doesn't even have to do a spindash.) Knuckles is a rogue, so he doesn't work with Sonic or Tails. Therefore, there are four types of games that you can play on Sonic 3: Sonic & Tails Mode, Sonic Mode, Tails Mode, and Knuckles Mode. (The last one is only available when Sonic 3 is hooked up to Sonic & Knuckles.) As a sidenote, you can hook up Sonic 2 to Sonic & Knuckles as well and play as Knuckles in the Sonic 2 world, which is by far the easiest way to go about the game, seeing as Tails doesn't have any unique abilities in Sonic 2.
The level select in Sonic 3 is next to impossible to input (the one in Sonic 1 was a little difficult, but possible, and the one in Sonic 2 was ridiculously easy) but not to worry! Sonic 3 is the first in the series to introduce game saving, so you won't need to worry about putting in a level select code in order to continue from where you left off.
Sonic the Hedgehog 3 is an instant classic. By taking advantage of the unique abilities of Sonic, Tails, and even Knuckles, you'll find yourself playing this game for hours. This game is from the Genesis era, so it's very hard to find, and so your best bet would be to buy Sonic Mega Collection for Gamecube. It doesn't matter which one you use because nothing has changed. It's a great game and deserves a place in your collection.