I have been a huge Sonic Fan since the Genesis days. I love almost all the 2D Sonic games and some of the 3D ones. Mostly up to around Sonic Heroes, I have not really liked much that has come after. But the GBA and DS series were a good throwback to the original gameplay that I loved in the series so I continued playing on with those.
I do enjoy Sonic Adventure 1 and 2 and think those really should be the model for the 3D games. Sonic often works best when it is kept simple and it remains mostly a platformer. I think when they attempt adding more gimmicks and gameplay options like characters with other various powers, using of guns and vehicles, or change the game mechanics away from running and jumping to something else entirely then the game suffers as a result. Many of the later games are like this, they require more than platformer mechanics and require things like riding on bikes and using swords to fight dragons, or transforming into were animals. None of these are really what Sonic fans are looking for in a game. This might actually contribute to the success of Sonic Heroes and why many people still consider that to be the last great Sonic Game. It brought everything back to the basics. You were on a track, you used the various abilities of your characters to make it across and your options were little more than running, jumping, climbing, or flying.
Sega Genesis was my first game console, so Sonic holds a special little place in my heart <3
Sonic 2 & 3 are my favorites. EXCEPT FOR THE RED BARREL in Carnival Night!
Yup I remember that being the stopping point for most fans until they figured out that it can be moved with the d-pad. After that the rest of the game was great but that little spot where you were trapped on the barrel was where the game ended for many people and contributed to not many liking the game overall as a result. Without it I think Sonic 3 is easily my favorite on the Genesis. I have replayed it so many times I know almost all parts of it.