Stu of Feeling Listless is thoroughly unimpressed by Heroes showrunner Tim Kring's account of his plans for the show:
Kring said no final ending for 'Heroes' has been conceived, noting, "We didn't have an island to get off of." On top of that, Kring noted that "My original idea was more of an anthological vibe to it, where you regenerate the characters."
Veiled Lost reference there. Actually, you did have a goal, a very good one, but you pissed it away at the close of season one. A surprising number of shows don't, but with a piece like Heroes you'd at least need to have a notion, simply because of all the characters involved. Audiences can smell when you don't know what your end game is. Look at The X-Files which began to look stale by the sixth season because we'd all worked out that Chris Carter had less of an idea of what his mythology meant than we did.
I don't see the X Files parallel, mostly because I don't think Heroes did set itself up from the start as setting out to solve a big central mystery. We now know that there have been people with powers, possibly triggered in part by a solar eclipse, for centuries. The task of working out why this happens could be used as the big goal in the show's final season, but it certainly isn't inherent in the setup of the show that everyone is trying to figure out how and why they got their powers. In The X Files, by contrast, it was central to the motivation of one of the two main characters that he wanted to solve the mystery of UFOs/government cover-ups/what happened to his sister.
I don't have as negative a view of Heroes as many online commenters. Season 1 was excellent, season 2 was wrecked by the impact of the writers' strike, and season 3 has introduced a major new bad guy who could well be around for years and is doing OK: I think we should judge it when we get to the end of the season.
Where I think the show's producers have a serious problem is that the economics and practicalities of running a TV series don't lend themselves to the "anthological" approach Tim Kring set out to use. In comics about a superhero team, the writers can easily push a character into the background for a while to let others take the spotlight: Marvel's writers haven't given, say, Nightcrawler a lead role in any of the main titles in years; he's been present in various teams, but usually in a background role at best.
If Marvel decided tomorrow that Nightcrawler was going to be the lead character in Matt Fraction's next big Uncanny X-Men story arc then they could make it so without much bother. By contrast, if the producers of Heroes were to drop the character of Claire Bennet after season 3 and then decided to ask Hayden Panettiere to return to the role in season 7 because they had a storyline where her character would have a key role then they'd have to deal with the possibility that the actress might not be available, or might be a lot more expensive to hire if her stock had risen in the meantime. They either need to have a lot more Heroes, so that no one character is essential to the show or has a unique powerset, or they need fewer Heroes so they can commit to following the fortunes of those characters.