It's a little different. Heroes is a drama, and Gilligan's Island is a comedy, for one. But in Heroes, 99% of them don't die no matter what happens to them. Therefore, the only reason it even matters if they save the world or not is for everyone else. What kind of drama is it where you throw all this conflict at people (who act as stupidly as Gilligan, for that matter) and then none of what they do really matters?
Honestly, while Sylar has been the only real redeeming character for a while now, having him slink away and survive in S1 (along with Nathan surviving as well) was the start of it all unraveling. Now, someone turns to ice and gets shattered to pieces and she doesn't die, and a few other instances that I can't remember off the top of my head where it's like nothing has a point. I know that comic books do similarly, but while this is based in comics, it's still a TV show. Besides that, they need to do something to mix things up and fast.
Their actions have to have some sort of consequences, which pretty much hasn't been the case at all for the past two years.
If it was me, I'd kill off most of the characters for real. Mohinder is dead weight now, as is Niki/Jessica/whatever her new name was, Parkman (because he's just so stupid), and a ton of others. Last season, they had the perfect opportunity for slimming things down, and they should've taken advantage instead of only getting rid of Nathan... sort of.
If it was me, I think the only ones I'd keep at this point would be Micah, Claire, Sylar, and Hiro, while at the meantime having a couple more origin stories (not told as poorly as the two new people in S2). Of course, Claire would need to grow up and get over her daddy issues for her to be interesting to watch, and I think having Ando die in front of Hiro, something that pushes him from bumbling idiot to more what future Hiro in S1 was, would make him interesting to watch as well. And how about some stories that aren't related to the Petrelli family?
...But that's just me. I just think there's too many characters with no real consequences and it's dragging the show down. That being said, I'll still probably watch, it's just not going to be very high priority for me to get around to the recordings, based on past history.