Less go!
For now I'll post my most favored.
1. Sonic Adventure for the SEGA Dreamcast (BEST): My favorite game of all time. The SEGA Dreamcast is the most remarkable system ever. Good times with this game and it just plays so great. Sonic's levels are the best and Tails', Knuckles', Amy's, Gamma's, and Big's are great as well. This game is the best ever!
2. Sonic Adventure 2 for the SEGA Dreamcast: My runner-up favorite. It's insane off the walls fun. Good times with this as well.
3. Sonic Unleashed for the Microsoft XBOX 360: Sonic's best game after SEGA went third-party. The reviews are just biased and Sonic's levels are just great. Good times playing this too....
4. Sonic The Hedgehog 3 and Knucklesfor the SEGA Genesis/MEGA-Drive: This one is really classic. Yeah, it's hard and can get more frustrating than the others, but I like a lot of challenge... even though it can take a while to get past some of the levels. But it's really well done.
5. Sonic The Hedgehog 2for the SEGA Genesis/SEGA MEGA-Drive: The sequel to the original Sonic the Hedgehog is even more insane in every way. It's an instant classic and truly made a Sonic a star. But this game does kinda feel a little bit more complex than the first one with the odd man out 10 levels instead of 6. Still excellent beyond recognition.
6. Sonic The Hedgehog for the SEGA Genesis/SEGA MEGA-Drive: The original Sonic the Hedgehog was awesome, man. Incredible and revolutionary way to start the best franchise ever.