I've decided that, between my assessments of the different characters, I will have interludes where I talk about something or other within Lost that either bugged me or that stood out as very interesting or important. First off...
The Problem of Walt
Who Walt is is relatively unimportant. He is the son of one of the other survivors, Michael, and it is through Walt's kidnapping that events are forced into motion with regard to the Others. Eventually, through questionable sacrifices, Walt is returned to America where presumably he leads a normal life. At this point, he largely disappears from the show (his last brief appearance that I can remember is in Season 5). But really, Walt isn't the issue here.
The issue is with the smoke monster. As I mentioned before, the smoke monster is able to take on the bodies and appearance of other people, and faces the survivors with these doppelgangers in order to judge them and also to lead them into chaos. In Season 6, we learn definitively that the smoke monster can ONLY take on the visages of people who are already dead. And this is where the problem arises.
Throughout the first half of the series, after Walt is kidnapped, he appears to a number of survivors randomly, without warning, and disappears just as quick as he came. This Walt apparition behaves much like the smoke monster does, leading the survivors into and out of danger on a whim. It leads Shannon to her death, and it also convinces Locke out of committing suicide. Through this, it is clear that the Walt manifestation has had some very important influences on the plot, and probably is the smoke monster's favorite form aside from Jack's dad, Christian. But this is Walt here. Christian is dead... but Walt?
Do you see the hole? Walt never dies in Lost. The smoke monster is supposedly unable to take on the forms of those who aren't dead. So... what the hell is that Walt ghost? Maybe I'm picky or perfectionist, but this really bugged me by the end of Lost, where most all other important plot points were given some form of explanation.
I tried to like Kate. I really did. That is because I think I know what they were trying to do with her and, in theory, it was good. Kate, I believe, was intended to be this strong and independent woman who relied on no-one but herself. She seems made to be the heart of the team, so to speak, and appears to always align herself with the team that is 'right'. I was astonished to learn that she was originally supposed to be the main character of the entire series. The only thing that prevented that from happening was the writers realizing that killing Jack in the first episode would make the audience feel betrayed for investing in his character. Thus, Kate was shifted to, arguably, the second-most important character.
However, in practice, Kate is almost always insufferably annoying. Her past is that of the fugitive from the law. On the bright side, this aspect of her character gave me a strong sense of her independence and self-reliance, particularly during her flashbacks. But this also gave her some dumbass need to be a total flake, far too often. The prime example is where, after many episodes of unresolved sexual tension, she kisses Jack in the forest. Afterwards, she looks at him like he has caught the plague, and then runs off without a word. Why? We'll never know. There are many examples; she often ignores reasonable commands to stay put in favor of going off and getting captured, she takes for-fucking-ever to decide between choosing Jack or Sawyer, and she never seems to actually fit herself in to the group of survivors.
I want to expand on that last part. Kate's character is very strange and unlikable to me primarily because of this. She is ever-present and often a central focus for Lost but, despite this, she seems to have ZERO relevance to the show. It seems like her only purpose is to prolong the relationship agony bullshit, flip-flopping from Jack to Sawyer, back and forth. She has barely any connection to any of the other survivors, and those connections that she does make seem to dissipate in short order. In fact, she only makes brief friendships with Sun and Claire, making both of these friendships because of issues of pregnancy and babies for each. Hmm; now there's a thought. Perhaps the purpose of Kate is to become more akin to the traditional perception of feminine norms; she makes a shift through the series from independent woman to caretaking mother. Whaaaat? Sexist writers!
More seriously, though, Kate seems like one of the weakest characters to me. She has little to do with any characters outside of the Jack and Sawyer love triangle, she even (perhaps unintentionally) interferes with Sawyer and Juliet's relationship later on. She consistently makes decisions on a "Born to Run" basis. She simply feels like she is there to interfere with the lives of other characters. Her decision to return to the island to help Claire, while noble, fails to keep interest. Right at the end, where you feel Jack has grown in character to the point of not wanting Kate anymore, they profess their love for one another and I just wanted to vomit all over the screen. Kate just isn't one of my favorite characters, what can I say? Maybe it was the actress? Or maybe what was theoretically excellent simply wasn't able to make the cut in practice. We'll never know.