Disgaea 6. For a series that's known for being funny and having entertaining characters, the game really did fall flat with a lot of its humor to me, and it didn't really have any entertaining characters.
Also, I really did not like how much they pushed you to use the Super Reincarnation gimmick. Like yes, I know Reincarnation is in almost every Disgaea game, but none of the previous games ever felt like they were trying to FORCE you to use it. I also do understand that almost every game seems to have a single gimmick they really push for, but they didn't really feel as... I think the word is intrusive? as Super Reincarnation.
So, for context, the main gimmick of Reincarnation in Disgaea is that you take a unit and reincarnate it into a different or better unit with better stats... but the catch is that said unit's level is reset back to 1. Which, if you like grinding for HOURS, that's fine, but I can only handle so many sessions of going into the Item World for EXP grinding before I lose my mind.
Thankfully, from what I've played of 7's demo, things seem to be a lot better now, but I was still very disappointed with 6.