They won't be getting rid of Sylar or Peter any time soon, I bet. I'm glad for that, as I think both are great characters, and have a lot more to contribute to the show.
No, season two wasn't that great, but it had almost everything working against it. Cast members changing their commitment at the last minute (Missy Peregrim), the writer's strike forcing last-minute script rewrites, and even Tim Kring admits that he made mistakes were made that he won't make again. I see no reason not to be optimistic about season three, especially since the focus will be on villains, and villains are my favorite part of superhero stories.
It'll be really great to see bad guys like Sylar and Elle get more screen time, hopefully along with villains they've been hinting at in the comics for a while now, such as Linda Tavara, EVS Dropper, and the Tenth Bride of Takezo Kensei.
I've also been looking at some of the (relatively mild) spoilers for season three at the
Heroes Wiki and to me, it seems to confirm that this will be the best Heroes yet!
EDIT: At the Jules Verne film festival, two promos of season three were shown - ones that contained actual footage from upcoming episodes. Someone recorded these as they were being shown and then uploaded them to Youtube; hence, the picture and sound quality isn't great, but it's better than nothing I suppose. Here are the links:
Promo #1:
http://www.youtube.com/watch?v=GZNS0pbzI6c&e
Promo #2:
http://www.youtube.com/watch?v=5iBLZ_4rTuQ
For a list of all the other spoilers known so far, check out the
Season Three page of the Heroes Wiki.