There is a pattern to a number of TV dramas. They start off with some great ideas, and give us a super first season. Maybe they still have some good ideas, and the second season is as good, or better. Then the rot set in.
The basic problem is that they are making too much money to stop, but the ideas have stopped flowing. And that's when they start jerking our chains.
What are the symptoms of this? Well, the main one is that they make us question what we've been told. They make good guys into bad guys and vice versa, and keep swapping them around. They go back and rewrite what happened in the past. They over-complicate stories, thinking that they are delving deeper and deeper but in reality just going round and round in ever-decreasing circles. They probably think that they are being terribly clever but they aren't, because they don't actually know where they are going or how to get there.
This phenomenon has come to Heroes in its third season with a vengeance. Part of this season is subtitled "Villains", but the whole premise of this season is that - apart from a few people who you know are good (Clare, Matt, Hiro...), everyone's loyalties, causes and essential goodness is brought into question. Is Sylar still bad, or has he turned? Is Peter now the bad guy? How about Nathan? Who are Clare's real parents? We don't know, and the writers keep making us jump from one side to the other.
Another symptom of this malaise is invulnerability, and I complained of this in my review of another show which went through this process (Alias - and Lost is another classic example). Characters keep getting riddled with bullets (or otherwise injured beyond the point of survivability), and miraculously come back to life. OK, in Heroes they had a reason for one of the characters, who had this ability - that's fine. But then they do the same with lots of other characters, through various means. It's a fake way of creating tension without expending your assets - and, crucially, without having to think of a smarter way to develop the story. What the TV executives don't seem to understand is that after a while, this means that we can't trust anything they tell us ("trust" within the context of accepting the story that they are creating), and therefore we stop caring.
The acting, production, stunts etc are still excellent, which is why I've reluctantly still given this season three stars. But I still rather wish they'd stopped after the second season (or even the first), and started afresh. I doubt whether I'll be getting season 4.