I've been playing Civilization 5 non-stop for about a week. I don't like it as much as 4, but that doesn't seem to stop me. This Civ series is seriously crack in video game form. I am currently recovering from a *massive* war against Japan. I'm a little worried about Bismarck, because the great wall of Germany is right up against my borders and I can see them amassing trebuchets and crossbow artists over there. It's going to be at least 12 turns before I can get sufficient defenses into that part of the country.
There's a map-type called Terra, in which you, and every other civilization, begin in "the old world," while a new continent -- full of barbarians and resources but otherwise untouched -- waits for whoever can get there first. I liked the idea of it, but I'd always win those games because, knowing it was there, I'd rush to gain the ability to cross the ocean. Now there's a mod somebody made called Terra Incognita, which is the same concept but about a thousand times better, because it generates a much more random "new world." You don't know what's over there. Could be continents, could be archipelagos, a few islands... might be nothing at all. It makes for a far more interesting game. So if any of you are playing Civ 5, may I recommend that mod.