Sonic the Hedgehog
This is pretty much the original of Sonic, and it is very good. You can only play as Sonic, but the gameplay is good, and the game as a whole is pretty fun.
Sonic the Hedgehog 2
Sonic the Hedgehog 2 is similar to the first one, only the graphics are marginally better, you can play two player and Tails (or in some countries he’s called “Miles”) is included in the game. This was basically an upgrade of the first game.
Sonic the Hedgehog 3
Sonic the Hedgehog 3 is an upgrade of the second. It is the same except for, better graphics, more stages, awesome music and the appearance of Knuckles. Still a good game, though. There is also the best song ever in it, listen to this!
Sonic and Knuckles
In Sonic and Knuckles, you can play as Knuckles and the graphics are better. A pretty good game.
Sonic and Knuckles 2
Sonic and Knuckles 2 is the same as Sonic the Hedgehog 2, just you play as Knuckles.
FAVOURITE: SONIC THE HEDGEHOG 3