Game-Breaker: Electrical Chainguns and high-tier Rage against non-electrically resistant enemies. Things just died horribly.
Narm: The opening monologue starts off with how Earth didn't see the invasion coming because they were too busy watching TV and downing prescription antidepressants, which is so ludicrous that it makes one wonder if Richard Garriot had a hateboner for consumerism or something.
Never Live It Down: Is this game known for anything these days except the fact they fired Lord British while he was in space?
Catharsis Factor: Genma and Soun finally standing up to Happosai after years of putting up with his abuse. Up to and including Soun banishing the little shit from the Tendo Dojo. After all the times where Happosai was canonically a Karma Houdini, this is a much needed change.
