I'd be hard pressed to think of a show that didn't take a few seasons to warm up. That's not to say they were bad, but it took some time for the actors and writers to figure out how the characters work.
The problem is less pronounced now that most shows are serials planned out years in advance, but it still happens.
Can't say I felt that with the shows I've watched in the last few years, like Dexter, The Wire, Six Feet Under. Some didn't even last more than three seasons, yet became classics, like Twin Peaks.
I've only seen Dexter from that list. To me, it took a few seasons to warm up. That said, it started out better than a lot of shows.
It's called "Growing the Beard", with Star Trek: The Next Generation and Star Trek: Deep Space Nine getting better around season 3.