Season 3, episodes 1 and 2 -- Did you See the Sunrise -- are, to me, two of the best episodes ever put on TV out of any dramatic series.
Season 1, as noted, is kind of spotty.
Season 2 gets running with some really good episodes, but season 3 is by far the best.
There are a couple of episodes that are Higgins-centric that are also VERY good.