A well done and detailed terrain says one of two things:
1. They're good at terraining/had someone terrain for them, but everything else is boring.
2. They put in the time to detail their terrain and likely put in time to detail the rest of the map.
Bad terrains destroy maps. Would Wow be half as impressive if npc names were all generic and boring? If the instances were monotone and the walls were bare? Gameplay is not enough. The environment is part of the UI. If the terrain is immersive, then the game will be more immersive. Why do people make triggered spells that do nothing but add effects to base spells? Why are people drawn in by these spells? They immerse you in a place separate from others.
Unfortunately, I tend not to play war3 in general anymore, though I always see your threads, and am impressed, at TWC.