The epic arcane caster in my campaign became very frustrated by the epic system. It is a big challenge striking the right balance. In effect, the way that epic is setup, as you scale above 20th, your villians and BBEG's gain more and more resistances and immunities, in order to be able to survive the onslaught and versatility now available to a party of epic characters. The arcane caster provides some excellent resources: divination at this level is extremely potent (if not one of the most important elements), versatility through buffs (especially high level defensive ones), transportation, and environment control. The npc's built up resistances and immunities, however, are a direct assault on the arcane caster's capabilities: direct damage, area effect damage, conjuration, charm/dominate, and insta-kill. As the levels go up, these become more and more to use with any degree of relevance. With the possible exception of the increased effectiveness and availability of insta-kill, your role is oddly diminished. It does seem somewhat of an unbalanced impact, however, when compared to Divine casters (whose spells primarily prevent and restore damage to the PC's).
My PC arcane caster found that was relevant through their breadth of knowledge skills (he was a M-U), his enhanced focus on divination, and the no save/no SR spells that attack non-resistance areas (rays, touch attacks, energy drain, waves of exhaustion, etc). This, in combination with the occassional complete domination with the ability to empower and maximize powerful AoE effects to devastate an entire encounter.
