Epic play is .... different.
IMO the epic magic is moot at less than ~35th level. Casters between 21-35 should get the epic metamagics and whatnot that increase the die caps, areas, ranges, etc. Early epic magic (35-50th level) seems only useful for getting past the non-epic spells that have no way to be bypassed; divinations that punch through mind-blank, for instance.
At higher levels....meh. It gives you a nuke to fire off when you have an opponent in a known area. Mass summons, eathquakes that can level fortresses, creating snowstorms in summer, etc. They don't take out the epic BBEG in most cases but smite so many minions that their threat is limited to their immediate presence.
Combat gets trickier. The creatures have so freakin' many specials, attacks and BAB that it really is just like 1st level all over again. I don't like the long, drawn-out slugfests so I'm leaning more and more towards crafting my own epic critters that have fewer hitpoints and more fast healing. They still have several hundred hp to survive non-epic foes and fast-healing 10 means that it heals 100hp/min, enough to appear invulnerable to almost any non-epic foe. Templates are a great way to get those epic CRs without adding hit dice.