My biggest gripe with the third Hobbit film was the scene where Legolas is fighting atop a ruined stone tower, a troll knocks the tower down, across a gorge...
...and it ends up lying still, like a bridge. I and a bunch of other civil engineering students saw it together, and at that point we all went "nope". Stone structures simply do not work that way. The tower should have broken apart under its own weight mid-fall. That's how poorly they can handle bending moments. The scene continued to violate basic principles of structural mechanics by having the walls of the tower break apart when orcs were shoved into them, but the "bridge" staying intact until held together by a single column. When Legolas was jumping from falling brick to falling brick as the "bridge" finally collapsed, we had all just stopped caring.
Also, earlier in the battle, where a bunch of elves ruin what would have been a perfectly defensible pike wall by jumping over it. Congratulations, now the dwarven phalanx serve no purpose, but also you can't retreat because there's a flipping pike wall in your back. "Hollywood tactics" doesn't even begin to describe it. Never mind the two thousand elven archers never even firing a single volley over the course of the entire battle, despite evidently having brought their bows and archery being their goddamn speciality.
I actually went to see the third film twice, but had to leave early because another appointment I had totally forgotten. That's when I realized that most of the plot of the movie is contained within the first 25 minutes.