I'm right with you on that. I could happily complete Knuckles' campaign, even though I knew it was harder, because I was able to get through Carnival Night. As Sonic, I was always stuck at the barrel until I figured out that you could get through by repeatedly bouncing with a bubble shield. It meant playing carefully to end up with a shield there, but it was possible. And Tails? Nah mate, I couldn't get his arse passed the Marble Garden 2 boss. Even when I did eventually manage that some years later, I knew he was going to get stuck at the barrel with no way to use the bubble shield. Knuckles' campaign is technically the hardest, but it was the only way that I could beat the game. I still remember the first time I got all of the Emeralds too.