Sonic is such an odd series where even the bad games are...oddly really cozy. I don't often go back to like Lost World or anything but 1-3k, Adventure 1 and 2, Shadow and 06 (usually with P06 these days), Colors (a game I don't really care that much for), Generations and so on and so on and so on usually find themselves in my play rotation at least once or twice a year
