It's a consistently great show that didn't overstay it's welcome and went off the air at about the right time. It's not without it's faults, of course - the first half of Season 3 is fairly slow and I dare even say a bit boring (although things really pick up big time at about the sixth episode) and Season 5 is an odd season because they split it into two "parts", but tried to pass it off as one season. The way it's written and executed, however, makes it feel like two separate 8 episode seasons rather than just one whole, 16-episode season. IMO, they really should have just made two 13-episode seasons and let the story flow organically instead of trying to cram too much into S5 and making it feel rushed, but oh well. They still managed to produce a great ending to the show regardless, though.