Even though I've only watched Seasons 1,2 and 5(have yet to see 3 and 4), Jack's character just really pisses me off. One reason that Jack pisses me off is that he is essentially an archetypical hero, albeit a wussy archetypical hero. I think that Jack's almost OBSESSIVE need to fix things just adds to his "archetypical wussy/wet-blanket hero-ness", and there have been plenty of badass archetypical heroes(Aragorn, Sawyer, Neo, Roland Deschaine etc) but Jack, no matter how much he tries(CIP his tattoos) will never ever be one.
List of things that irritate me about Jack
1. He's so obtusely stubborn. One example of this is his almost steadfast refusal to regard anything of what Locke had said about the Island to be true in any way, shape or form. The only reason Jack shifts to being a "Man of Faith" was guilt over not listening to Locke earlier. Also, when he's with Achara, he pretty much beats her around the place until gives him a tattoo, which is yet another example of Jack's stubbornness(one example of many)
2. When Jack was pretty much in charge, he didn't really include everyone in the group, unlike Locke during his spell as leader in Season 3. Wouldn't one of the marks of a good leader be involving people in the group/making them feel valued?
3. The whole Mr.Fix-It thing. Yeah, I know that he's a doctor, but he takes his need to fixing things way too far. Seriously, setting off a hydrogen bomb just to prevent them from ever going to the Island in the first place?
4. Is it just me or does Jack just overreact to certain things?
5. Jack's development as a character(or lack of it). Jack is, in my honest opinion, the exact same person that he was in Season 1, all that's changed about him is the shift from "Man of Science" to "Man of Faith", and that shift was brought on by guilt. It might be the fault of the writers that Jack is so much of a one-note character.
6. Jack will never compete with Sawyer, Locke and Sayid
7. His "daddy issues" and his angst. Hey, so what if his dad wasn't perfect, no parent is perfect. Also, Jack accusing his dad of sleeping with his wife was a "dick move". It just bothers me that Jack wasn't willing/or able to attempt to repair his relationship with his dad.
Sorry if I may have offended any Jack fans here