I changed my mind in a negative way about GoodFellas. I used to love it, but I watched it a while back and found it tiresome.
Joe Pesci may be everyone's favourite in the film, but he's the least threatening man in the world. Having a little squeaky Italian threatening to fuck people up looked laughable when I rewatched it. On top of that the main actor (I can't even remember his name) is bland and wooden, and DeNiro is either wasted or not trying, or both. Why hire an obviously Italian-American actor to play an Irish-American? It's confusing that they won't let him be a proper Mafia member because of his heritage when he looks like he could be one.
I appreciate that at the time a film showings mobsters juggling their crimes with mundane family life must have seemed revolutionary, but it has been spoiled by too many imitators, and in this post-Sopranos world it just seems run-of-the-mill. Of course that's not the film's fault, but it made it harder to enjoy. It was odd how lots of bits I use to love when I was younger just looked shit. Of course I might watch it again in a few years and love it, who knows.
I had the opposite experience with Alien. I had seen Aliens as a child, and when I stumbled across Alien last year I thought it was the same film (mists of time and all that). I was expecting an action film about Space Marines blowing away aliens, so I found it quite underwhelming and a bit dull. "Well that wasn't as exciting as I remembered. And I though there were more aliens in it than that," I thought to myself.
Later on I saw Aliens, and realised that was the film I'd been thinking about the whole time. Everything was there, the Marines, the shooting, the dozens of aliens. And do you know what, I didn't think much of it. So then I watched the first film again, knowing not to expect the shoot 'em up I had previously thought it was, and ended up loving it. All those people who say the second film is better than the first are wrong.