X6 is a frustrating game actually. It brought the X series into some of the cheap death designs of the NES era so its often considered to be one of the hardest entries barring X7's bad 3D controls *shudders*. So most fans hate it, especially since X5 was meant to be the final X game, though X6 actually ends in a way where its still canonical with the MMZero series depending on the ending you get so I still count it as part of the main timeline. The game is seriously designed to piss you off though.

I like Killer Instinct but it never kept my interest as a game and had some bad balancing issues. I still enjoyed it though.

I've never played much of Disgaea 2, and to be honest, the series never caught hold of me like other SRPGs have. Its funny and I love the characters, but the gameplay always felt more like busy work.