I've always been hard on the side that the fluff the players and DM make is automatically ranked over the default fluff. You want your Rage to instead be a stance of perfect calm, where you carefully analyze your opponents to find their weak spots? Sure. Your "monk" is a rowdy pit fighter who throws wild haymakers? Great. Your wizard is actually throwing out a self-propelled bomb that explodes for 8d6 damage? Go for it. I'll usually talk it over with the person beforehand, of course, and there's probably some lines that'd go too far for me (if your wizard is pulling their robe down and farting instead of casting stinking cloud, that's probably not happening), but for the most part, I want my players to be able to make the characters they want. The system is just a tool for them to use.