Sword Art Online only has one season, and it was bad from the start.
Durarara!! only has one season, but the second arc wasn't as good as the first one.
Death Note only has one season, and the last arc was perfect setting for a perfect ending. Only ones I see *****ing about it are L fanboys.
Darker than Black: Ryuusei no Gemini isn't as great as the first season, but still good. Hei was desperate, but he overcame his hardship and that's what we call development. Powerless? Hei achieved the reputation of being the strongest contractor way before he obtained electricity.