Are you referreing to a blue sea, green sea, sea shore level, coastal shore, irrigated land, plains, deserts, hills, mountains, troposhere, mesosphere, exosphere type of altititue? That would be one complex system and you would have to throw out the square analogy and start describing tiles as cubes.I'd like something closer to Alpha Centauri: with actual altitude for each square. This could lead to more refined terrain types combined to climate.
I would like to be able to step on Antartica like all the previous Civilization games. Although the north pole really has nothing to step on except ice. The Arctic ocean is just a minor distance for Canada to attack Russia.Also being able to step on the poles... that would lead to an something lika spherical map, but I'm conscious of the difficulty of combining a sphere but the solution is simple: a huge polyhedron.

I woud prefer the next franchise to be a little less demanding. With a 1,5ghz with 1 gig and a good 256mb video card civ IV became awfully slow in late game, even on a standard map - and that was better than minimal syst. requirements. Cutting in the detail of terrain, units or ressources to go for a more schematic appearance instead would make all more fluid without requiring a gaming pc (which is what I had, though a very little older than what was sold when the game was released). Normally a Civilization player is not looking for a graphically realistic game, but for a totally brillant concept with a refined interaction of rules. Remember: I got addictited to Civ.I on a Mac SE.
You think a standard map in the modern age is slow. Go try the huge earth map with 18 civs in the modern age and then you'll find that one turn is enough time for you to toast lite bread, put on some butter and pour a glass of pop. I haven't tried going to the corner store for one turn yet but later perhaps.
I liked Civ3 because the game was not as computer resource demanding compared to Civ4. Hey, computers need to get upgraded some day in it's 3 year life cycle and you'd might as well do an upgrade or buy a new system for a new game than anything else besides a new operating system.