Yes the pilot episode had its flaws, no arguing that.
The S1 episode with Joan Jett showing up as a psycho-femme fatale immortal was awful
Constantly leaving Tessa at home while he goes off to fight the villain of the week got old quick.
Bad Day in Building A was an episode where Duncan got to show off more of his other skills and to face off against non-immortal enemies without giving away his secret. A step in the right direction.
Halfway through Season 1, the episode where Grayson and Darius were brought in and Duncan shifted his operations to Europe was where the show started improving.
Episodes of Season 1 to watch due to being pretty good or also expanding on parts of the mythos:
ep 2: Innocent Man: shows Duncan's code of honor and that he will go out of his way to save an innocent. Also a funny tagline at the end of the fight "In the future I'll remember to leave your friends in peace." Duncan's response "What future?" and beheads him with a vengeance
Ep 7: Mountain Men
Ep 8: Revenge is Sweet, Duncan tries to run away before the quickening over takes him showing that there is no escape from it.
Ep 9: the Sea Witch: shows that proximity counts even if you don't do the beheading
Ep 11: a bit weak but does confirm that all immortals are foundlings/orphans
Ep 13: Band of Brothers. Grayson and Darius are introduced into the series along with the concept that Grayson being an "ancient" immortal (almost 2000 years old) could be an automatic win against Macleod who is only 400. Also the concept of Light and Dark Quickenings is mentioned
Ep 15: immortal Xavier St Cloud (Roland Gift of Fine Young Cannibals) plays the latest immortal villain. He escapes Duncan after being "disarmed" and returns in Season 2. He would also appear in later episodes in flashbacks. This ep shows that immortals do NOT regrow lost body parts........though it also did not show if they could reattach the lost part and hope it regenerates back in place.
Ep 18" Lady and the Tiger: first appearance of Amanda, 'Nuff said!
(Also shows that the Quickening goes to the one that does the beheading, not necessarily the fighting)
Ep 22: the season finale: The Hunters we also get Hugh Fitzscairn played by Roger Daltry of THE WHO. Also the loss of a good character, but that was due to the actor dying.