Personally, I'd like to see a few more "alternate realities" and races added to the game.
I'm not talking a ton of them, but, perhaps a "Plane of Fire" with a fire theme (seas of sulfur, volcanoes, lots of random fire monsters, etc), Plane of Earth, Plane of Death, etc. There could be 1 for each major greek element (Earth Fire Wind Water), Each Japanese Elemental (wood, fire, earth, metal and water), or each spellbook (maybe a very high spell for each "type" would open a portal to their repsective planes, whereas the others would have to capture a portal from the map). Maybe spells would have different effects on these planes -- Some wouldn't work, some would work differently, etc. For example, Wood spells wouldn't work very well, if at all, on the plane of fire; or Fire Golems would get extensive bonuses to their stats on that plane.
Perhaps that could even be extended further, with an "extended mode" where AI opponents could start on these various planes. Would be interesting to have some ancient necromancer's forces start spilling into "reality" from the Plane of Death in the middle/late game, for exmaple; or perhaps a "Planar Cold War" between several warring mages covering several planes.
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