When LOST ends on Sunday, people will inevitably be disappointed, possibly even angry. This isn't just par for the course regarding this specific show, it's part and parcel of the event finale. Hopefully, they've paid attention to some past mistakes.
The event finale is pretty rare and anticipation is generally proportional to aggravation. We all have a sense of what this kind of finale should be and what it should contain, we have a concrete stance on how the series should wrap up. In this respect, Damon Lindelof and Carlton Cuse might be in a little trouble, considering that fans of the show have been predicting the outcome since nearly the very beginning. But even without massive expectations to live up to, event finales often fall short, and they do so by making these specific mistakes:
1) Getting too introspective.
The Seinfeld finale has been almost universally hated since the moment it ended. It wasn't funny and it relied heavily on the trope of trotting out pieces of the show's run to keep the audience engaged. LOST has already brought much of the cast back for cameos, so they won't be contending with a never ending line of returning characters. But Seinfeld also looks within for the context of the whole show. It teases multiple possible endings (Jerry and Elaine getting back together, Jerry and George moving to LA) and is seemingly worried the whole time with legacy, specifically the legacy that the New York Four have espoused throughout the show's run. The finale is really a referendum on the content of the entire series and on the attitudes and actions of the main characters. Since LOST is largely preoccupied with these sorts of large moral issues, it's a fair concern that the finale hits this hurdle.
2) Getting too sentimental.
The ultimate sentimental event finale is surely MASH, it had become so weepy in its final years that a real tear-jerker of an ending was inevitable. It's doubtful that LOST will end in a such a way, but sad goodbyes are a possibility, especially if someone (Jack, it seems) stays on the island forever while everyone else either leaves or dies.
3) Killing everyone off.
It's a pretty tempting thought to just end everything as definitively as possible in a finale like this one. This isn't Sex and the City, there isn't a life-after-TV movie franchise in the works for LOST and Lindelof and Cuse have made it clear that they're ending the story. And that's fine. But killing everyone off can really backfire, as the Six Feet Under finale proves. For a show about death, it seems appropriate to have everyone kick the bucket before show ends, but it destroys all the enjoyment. We've been sitting here hoping that our favorite characters make it out of the series alive and if none of them do, all that watching will truly have been for nothing.
4) Getting too fancy.
When something is as anticipated as an event finale, there's a tendency to get a little fancy. David Chase got really fancy in the final moments of The Sopranos and the whole world turned on his show because of one little decision to not have an actual ending. You never want people taken out of the moment so much and calling around to see if that actually happened or if they need to make an appointment with Time Warner. LOST can be extremely adventurous in its film making at times, but hopefully it won't be right at the end, there's simply no need for it. We've come this far and, at the very least, we need to leave satisfied. This means an actual ending with a nice long fade to black.