2nd edition has a lot fewer dimensions of complexity, making the task of running that campaign a lot easier on him. It's a very dangerous edition where even epic-level characters can realistically bite it to a single failed save versus poison. Factor in that most high-level spells take longer to cast than someone running up and hitting you with a sword, plus the fact that a large number of high-level spells actively encourage the GM to screw with you, and it's not difficult to challenge the players with a block of stats that has three to four curveball abilities.
That amounts to a lot more time spent developing the story, and it still remains easy to improvise if something unexpected happens.
Smash-cut to 3.5, and we have characters that are not just able to do anything in a single turn, but everything within a single turn (or less than that, with things like Celerity, Contingency, Time Stop, and other planes with alternate time traits). Preparing a proper and engaging challenge ahead of time for such a character can take weeks, which are weeks not spent developing the plot, and your GM's improvisational skills which had once been adequate are now limited to kludgy impromptu meganerfs because no easily-conceived threat can harm you otherwise.
Again I urge you to talk to your GM; he's in over his head (and again I expect you'll give us no indication that you have done so, or that you even read my lengthy rants )
The most elegant solution I can think of is a Co-GM; your current GM manages the story and background of the villains, and delegates to the Co-GM by describing them. The Co-GM then does the legwork in mechanically designing these villains and devising what strategies they might employ even before they roll for initiative, since pre-fight planning is a huge factor in epic levels and the villains must be able to do the same.
Even then there need to be limitations beyond just the written rules of the game, because once a character or villain makes the leap of living in a fast-time demiplane and acting only through his army of deific ice assassins it truly does become calvinball.