Then today Civ 5 got announced via GamePro.
The most significant change from an aesthetics standpoint is that after about 8 games (counting both core and spin-offs) they're switching away from the grid system and going to a hex-based map. This will certainly make the city radius look more natural, but it's going to hurt my brain for awhile trying to adjust my thinking. I've got the 5x5-with-corners-missing plus shape embedded somewhere in my brain from almost 20 years playing the franchise, and despite being simpler in theory i'm going to spend a long time staring at the hex map thinking "if i place the city there, will that resource be in range? And where will the next city go if i'm tiling them properly?"
And i'm pretty sure that using a hex board it will be possibly to tile cities perfectly, something you couldn't do with the grid map, and i actually think that might be something of a detraction. You certainly can't tile cities perfectly in real life, even ignoring "trivialities" like terrain and roads. It seems pretty natural to me to have to decide between placing cities so close together that they're competing over some resources or far enough apart that there's still a little space left between them (even if only on the corners.)
And i've got to say, if too many games start going the hex route someone is going to have to come up with a hex-based spreadsheet program so i can map out my strategies accordingly :)
Edit: Ooohhh! GameSpot has a (single) screenshot!