I always, ALWAYS try to Spin Dash in Sonic 1.
F*ckin' stupid game not magically having the perks of its later sequels. F*ck they tryin' to pull?
The biggest obstacle in Sonic 1 isn't the enemies; it's gentle but steep hills. Bananas.
I'd still rather play most Sonic games than most Mega Man games, personally. I like Mega Man, but I'm not comfortable calling my video game a "Cheating, c*nty sack of assholes" as often as I end up doing when I play Mega Man games.
I think you'd dig Sonic Adventure, or at least the Sonic levels. Mileage varies on the side character levels. I find them a nice break, but some people just want All Sonic, and I guess I understand that. I will say that the Sonic levels in SA are some of the most fun I've had playing Sonic games. They're all the fun parts of Sonic gameplay and none of the frustrating parts. They could be longer, and there could be more of them, but they're fun.
As I've said elsewhere, though, if you only ever play one Sonic game again, forever, play Sonic Generations. I can't recall one single thing about it that I didn't like. I played it on Xbox 360, so I had the added benefit of creating a custom soundtrack for it full of tons of speed, thrash, and hair metal.
It's bliss. You haven't lived until you've played Sonic racing down the side of a skyscraper at a billion miles per hour with swarms of robots in hot pursuit, to the strains of Fozzy's impeccable cover of "The Mob Rules".
Seriously, it's a really good game. I'm amazed it doesn't get more discussion.
I also liked both parts of Sonic 4.