Heroes is always the first show I think of when it comes to fumbling later seasons.
First season is really good. Apparently they had planned to have the next season focus on other characters, which could work really well. Let's introduce some new blood with new powers, and occasionally have one of the original characters pop in and do stuff.
But the producers wanted more of S1's characters, they were the popular ones. So they had to keep finding shit for them to do, while neutering Hiro in various ways since he could fix pretty much any problem in an instant. It became what cape comics are at their worst - a meandering mess with characters changing sides and dealing with dumb drama while never being in danger of actually getting killed for good.