LoTR and Donnie Darko I enjoyed upon seeing them, but on reflection think they were pretty dull or bad. LoTR has a lot of ground to cover, ground I've admittedly never read the source material of, but it can drag on for so damn long. It also comes across as being unnecessarily hammy at times. I remember watching Return of the King with a couple of housemates at uni and we spent most of it making fun of what was going on. In LoTR's defence, it does have a spectacular scale, but I don't believe I could sit through the trilogy now 'seriously', whilst I could probably enjoy it considerably if I was able to sit through it mocking it. When it hits its stride though, it can be great.
For Donnie Darko, my problem is the choice at the ending. Putting aside all ideas of time travel, because the whole damn film is so bloody weird that it feels perfectly acceptable, [spoiler]the fact that at the end he's happy to set everything right...but let himself die?[/spoiler] Perhaps it's supposed to be a great character dilemma - how do you know what they're thinking? And so on. My problem with that is that there is no indication prior that he would even consider this as a course of action to take. Sure he has some problems, but it just seems odd. There's absolutely no reason why he couldn't have done all he had and averted his 'fate'. For me, that undoes a lot of the film. The more I've thought about it, the more I've disliked that too.
Despite that, I enjoyed a fair bit of the dialogue, the tone and characters. Also, I'd be far more willing to sit through it again than any of the LoTR films because it's been a good few years since I saw it and I might have misunderstood some of the content when I was younger. I wouldn't be surprised if I missed something integral to the ending that I've discussed, although I don't believe that's the case.