I actually though three was the best season. But really if you start with the last episode of 1 and watch til the next to last episode of 5, you miss most of the facepalm, though there are throwaway episodes.
Season 1 got better when Darius was introduced, too bad the actor's death forced some rewrites as Darius was never meant to be killed by the Renegade Watchers.
Season 3 gave us the origin of his katana and why he uses it as well as the villain Kalas and how they had their final fight on the Eiffel Tower, the world's biggest lightning rod
Season 4: Dark quickening and the Watchers putting Joe on trial
Season 5: the Four Horsemen and revelations about Methos.