To this day I think Luigi's Mansion 3 might be the game I've finished that I enjoyed the least. I loved the first one (and liked the second one well enough, even though it was a bit watered down for the 3DS), just so we're clear.

The simplified ghost catching mechanics made most of the game's fights pretty boring, the Gooigi puzzles almost always boiled down to "I need the strength of two vacuums" or "I wish I could fit through this grate". Also, the last boss was godawful.

Most egregiously, I think LM3 might be the most filler-stuffed game I've ever played. The number of times you get an elevator button only for the game to go "Haha, no" really started to piss me off. The second time fucking Poulterkitty showed up, I actually looked up a walkthrough to gauge whether there was little enough of the game left to warrant finishing it - I wanted to stop right then and there. I think Nintendo took the criticism that LM1 was too short to heart. The thing is, without all the padding, LM3 would still have been a perfectly reasonable length (maybe even still too long). With all the padding, it was an utter slog.

Edit: Also, as an inverted aiming enjoyer (there are dozens of us), why the hell can't you invert?