It's very good, but the ending was very divisive at the time and so it gets a lot of hate too. I think the show does fall off a little bit near the end, but the first and second seasons are some of the best television I've ever seen.
I remember watching the finale live on television and thinking "oh boy, let's see how many of the remaining 13,523 mysteries finally get explained!" And then the ending was like "the real explanation is the friends we made along the way."
The issue in real time was years of the show runners promising over and over and over that "every mystery will be answered, and there will be no loose ends after the finale, and we already know what the end is going to be, just trust us".
People were extremely hyped because dozens and dozens of mysteries were generated over the seasons, so to tie them all up would be incredibly impressive.
Unfortunately it was blatantly unrealistic for that to happen, and there are several examples of the writers not having a clear direction and just stringing the audience along by creating more mysteries than they could possibly solve to add "suspense".
Two decades later it's sort of a different experience watching the show on its own terms.
Yeah you really need to watch the finale on its own terms. People got so hyped that literally everything would be explained in a character-driven show. However, there are actually relatively few mysteries left unexplained by the end, just about every mystery in the show was explained by the end. The biggest issue with the show is that it wasn't written out fully to begin with, which would have allowed every loose end to be tied up, but given the television landscape of the mid-2000s, that never could have happened. It's because of LOST that we have shows that can do things like that today.
It's fine on its own terms and I never really hated it as bad as others. I blame the producers for going on the record over and over and over saying that everything would be resolved and answered. Most of the main points wee fine, but there were a good handful of story threads that were dropped lazily before they even came close to a resolution. They were not particularly respectful of their audience, although it's true that it's influence on prestige TV was overall positive.
It's... interesting. Like a genuine cultural artifact, but not conventionally good. I really like it to be clear. The plot is kind of insane and all over the place, but it also has this uncanny knack for always answering 2 previous questions, and raising 3 new ones. The cast did a phenomenal job, and I don't think any other TV show has ever captured me in a "I need to tune in next week" kind of way.