Boran - obviously the random map generator can be turned off... it's called playing a scenario. Playing a scenario set up in the right way is no different from having set maps like Dawn of War and C&C Generals. A random map adds so much more replayability to a game. Sure, people can make new maps all the time, but playing on a mirror reflection equal-opportunity map just isn't much fun for me in the end.
I much prefer a random map. Sure, occaisionally people get a bum deal and the terrain is against them. That just means you have to prove your ability even more! The terrain won't be against you every game, some games it will work in your favour.
Saber - as Viceroy pointed out Age of Mythology had a random map generator - one of the best and fairest I might add - and it is 3D.