High level d20 non-D&D games - how do they hold up?

[Kunimatyu]

Theoretically True 20 should hold up at any level. I've heard people complaining about the spell users at high levels though. They say the damage output of an adept far outclasses any melee type.

If you allow Elemental Blast as written, yes. If there's one element of True20 that needs to be toned down, that would be it(The other damaging powers are fine, though).

Reworking the blast to deal +1 damage for every 4 levels of adept + your key spellcasting stat, and have it ignore armor and natural armor bonuses to Toughness would bring it in line, I think.