Totally, completely, utterly broken ~ crashfest. Rename 'One more turn into One more crash'
The combat is much reliable, no more losing modern units to far older units that have crazy stacked defensive bonuses. The fighting now is much more tactical, no more stacking tons of units to defend your cities, everything now requires you to think and plan your strategies, which makes the game feel slower paced than the previous games but more than makes up for it in many other areas.
The UI has been simplified, but remains highly functional and everything is crisp and clean; in DX11, it looks very nice indeed.
There are many new elements in the game such as natural wonders and non-player city states in which you can either conquer or be-friend, either of which will give your civilization a nice bonus, the old social panel has been redone and made into a social 'tech' tree, allowing you to fine tune your civilization.
I would still like to see more future tech though, I guess that is because I still love 'Call to Power', and I think it wouldn't hurt to for a future expansion for Civ V to expand into the future.
The biggest problem with the game, and unfortunately after months of promises and patches, the now infamous C0000005 crash still hasn't been fixed and very much doubting it ever will, meaning large map/epic games will eventually result in many many crashes which seriously diminishes the quality and fun of the game.
Editing my review after several years, lowering score down from a 5 to a 3 because of the sheer amount of bugs and crashes still present, and many updates Civilization V is still a major crashfest, and with new DLC and an expansion coming out, looks like Firaxis is just stealing money now, earlier today I tried to play again ~ and the game still is virtually unplayable, I have yet to actually finish a game at least with Civ4 you could actually reach endgame.