Heroes started out amazing in the first season. It kept us guessing at every turn and showed superheroes in a way that hadn’t really happened before on TV.
This one may be controversial because a lot of people really like the show and series but The Walking Dead didn’t maintain the quality it had in the earlier seasons.
I don’t know if I even need to explain this one at this point, but here goes: Game of Thrones arguably has the best first season of a show ever made and one of the most disappointing endings.