The first three seasons are definitely the watch worth. The Costa Negra story-line in the first season is on the same level as the last episode of Blackadder Goes Forth. If you don't get the reference, watch both series.
It becomes quite clear early in Season 4 that they started running out of ideas. Most American series run into this at the same time, with many overstaying their welcome for several seasons too long.
Review of Major Dad
