I watched seasons 1-3 in the summer of 2008 when I was kinda bored (my scholarship allowed me to take 12 credits in the summer semester for free, but $995/credit for any more than 12, so I took only 12 which is way less than a normal semester for me so I had a lot of free time).
I had a love/hate thing with Mad Max. I thought the renegade post-apocalyptic thing was such a cool setting for a movie, but the plot was just not as good as the setting was. You had this really interesting guy, in a really cool setting, and then it was a totally dumb movie.
With Lost, it was a similar feeling (but to a lesser extent). The island was cool as fuck. I mean, that island setting felt like something out of a Dark Tower book. Just layers and layers of mysterious things going on. Like it's this island that's half magic and there was important stuff going on but you don't really know the whole story behind it, but you figure it out piece by piece.
What turned me away from the show was a few reasons.
1 - I got tired of seeing character flashbacks. While they were somewhat interesting in that they revealed a little bit of the characters' pasts, there were so many of them and they were so long that it just got boring.
2 - I got tired of drama between the different characters. Again, this is something that is good in moderation, but they had a lot of it.
3 - There was very little plot progression, and very few mysteries revealed. Maybe I'm impatient, but I wanted to at least figure out a few things about the island. I watched almost 72 hours of it (for comparison, I estimate that it took a similar amount of time for me to read the entire Dark Tower, or the entire Sword of Truth, or read the Silmarillion, the Hobbit, The Lord of the Rings, and then watch all three movies)
I guess, in sum, what I didn't like was just the length of it. The main plot (figuring out what the deal with the island is) was completely overshadowed by all sorts of subplots, and I just got tired of it.
It was like the Wheel of Time. They create so many characters with so many backstories that by the 12th or so Wheel of Time book, you'd read a 1,000 page book that would really have almost nothing actually happen in it, because each main character only got a couple of chapters about them, since there are 25+ main characters.