Final verdict: Not worth it.
The first season was fun, but it went downhill from there. The last season threw away the hard work of the first season or two, and the last episode just blew the whole thing.
Mild spoilers under the cut. More ranting than discussion, but if you want to remain tabula rosa, don't follow...
The fun part of Lost was watching all the characters interact during, before and after the crash on the island. The mystery of the island itself was a driving force, shoving the characters together, apart and away.
But none of the mysteries were ever solved. None. Some of the questions were answered, all of which led to other questions, but at no point was anything ever explained.
And, as it turned out, my prediction as to the actual circumstances of the survivors was dead on. But done so poorly. The last episode of Lost will rank down at the bottom of finales with Battlestar Galactica. It would have been better if they'd ended the series abruptly at the penultimate episode, leaving everyone hanging like with The Sopranos. By making the attempt, and failing, the whole series was just wasted.
The show's set pieces went from being flashbacks to flash forwards to flash sideways. But in the last few episodes, as the timelines nominally "converged", people kept asking, "Do I know you?" From the previous seasons, we know they did. All that hard work of following the characters just went down the drain.
I will say that I ate up the episodes like candy. I (and eventually Carole) would insert a DVD and watch two or three or even four episodes in a row. Part of it was that the DVDs were in HD and I didn't have a digital cable connection at the time, so Lost was shiny. Part of it was that without commercials, I could see three episodes in the space of two broadcast shows. And part of it was being able to turn on Closed Captioning and pausing and such, plus viewing the extras.
Many of the extras were fun. My favorite is probably from the second season (I think), where they talk about the guy who's job it is to track the guns. Firearms get taken, leant and stolen, and making sure that Character A is carrying Weapon B is a major continuity problem.
I can't say I regret watching the thing, but I can't recommend anyone else does either.