I'll go first. Mine is that I can't stand the Deadpool movies. They are self aware and self referential to an obnoxious degree. It's like being continually reminded that I am in a movie. I swear the success of that movie has directly lead to every blockbuster having to have a joke every 30 seconds
The Dark Knight has fucking terrible editing and a lot of bad, hammy acting. The opening bank heist is just bad, with really on-the-nose dialogue delivered pretty badly...even William Fichtner seems like he's trying a little too hard, and he's an otherwise good actor.
I know the editing has been covered in some YouTube essay that made the rounds a number of years ago so maybe that's not such an unpopular opinion, but it really sticks out to me like a sore thumb.
Before anyone gets totally mad at me, I still enjoy the overall story, a lot of the action, and I think both Ledger and Bale (dumb batman voice aside) are great. Also, Morgan Freeman, Michal Caine and whatshisname who plays Harvey Dent are also very good too.
I actually fell asleep watching The Dark Knight in a movie theatre. They fucked up the pacing.
Another instance of this is the second Spider Man (the one with Doc Ock). It was so sluggish that I forgot there was a villain halfway through the movie. Then it cut to Ock doing something and I was like "Oh yeah, that guy still exists".
Another unpopular opinion I have is that spider-man 2 is pretty good, but not on the level people seem to put it on. The train fight is good, the overall plot is decent, Alfred Molina is a good choice as Doc Ok, but the whole split personality thing came across to me as kind of cheesy. At least Willem Dafoe's scenery chewing in the first movie was highly entertaining.