Sonic 2 is a pretty good game, though in my opinion S3&K is much better. Sonic 1 was my first Sonic game.
The things that I don't like in the game are the automatic super transformation in the air after a single jump. The only way I have to try and get round it somehow if possible is to spin dash up a slope, or spindash off something, hoping to bounce on the enemies below me. Also some of the levels were too short, and needed to be bigger. The 1st acts of Chemical Plant, Aquatic Ruin suffer from this the most out of all of the stages. Also if Tails can fly after he died or if you left him behind, then why couldn't you do it in gameplay? which is one thing which annoyed me when I first played the game and kind of made Tails not that exciting in 1P unless you want to run through 1P with him for the fun of it. When Sonic 3 introduced Tails being able to fly in gameplay, I played as him much more than I did in Sonic 2.
Though what I do like about the game is the nice colourful environments as you go through the game, music was quite cool, fairly challenging in some areas, and unlike Sonic 3's a decent 2P mode, though it couldhave more stuff in it.