Have you ever played Moose's terratek battlezone? It has square tiles and without proper micro it is nearly impossible to win. Maybe someone should make a map with varied high, low, doodad terrain.
Hmm I would like to see that square tile map. Mostly I think that iso just makes the terrain look better and be more realistic because that is how the terrain was designed to be and how it always was.
Extended terrain would sure help keep it looking good. You wouldn't need square tiles to do that.
As long as it keeps the terrain still balanced I think extended terrain would be good. Like if it didn't mess with accuracy %'s on high and low ground and such. Though I don't think say a waterfall would automatically make a map the greatest, it would just be thought of as a doodad type thing. Just meant to spiff it up a bit.
Waterfalls dont work in melee maps though.