Here is my verdict:

Technical performance: Had some problem with the demo, but the retail version is remarkably stable for a newly-released game.

Menu and Startup interface: I miss Baba Yetu, but the opening video is good enough for the first time.

Gameplay interface: Well, you should expect an improvement after six years of technical development. Miss the globe view, though.

Sound and soundtrack: The symphony soundtrack of mid-game Civ 4 was great, (though the modern soundtrack was painful, and burdened the game with royalty costs). Civ 5 is a step backwards when it comes to music.

In-game effects: Askia posing in front of a burning castle is more bad-ass than ever in Civ.

Civilizations and Leaders: The lowered number of leaders is not that bad of a loss. But Inca, Spain and Mongolia seem more deserving than Iroquois, Ottomans and Siam.

Unique abilities. I have always had issues against these features. Not only that they are racist, they also challenge balancing, and are simply non-adaptive (since you choose nation without any gameplay information).

City-states: I agree that they are broken now, but that is a balance issue easily solved by a patch. And I just love when they all go to Permanent War against an evil conqueror.

Hex map: Instant success.

Included units: So far I haven't played a modern war. But modern and sci-fi weaponry should preferrably wait for an expansion pack.

Land combat system: There are some strange things (Archers shooting further than modern infantry), but in general it is refreshing.

Naval: Embarkment is a great feature, and should have been included in Civ 4 (as Rise of Nations introduced the concept back in 2003).

Air: Haven't fought an air war yet.

Resources: In Civ 3 & 4, a large civ had the opportunity to use one single source of Oil for its entire army, dooming small civs. Not all resource issues are solved, but at least they are less broken now.

Cities, Buildings and Wonders: Lots and lots of buildings are needed now, and micro-management is apparent.

Roads, Rail and Terrain improvement: I want to road every tile, and railroad at least the industrial tiles, and make a profit from there. That opportunity has been stolen from me. They have also missed the opportunity to merge the Worker with the Workboat by using Embarkment.

National happiness: Reduced micromanagement is good. It also lays a burden on large empires.

Economic system: Has gone backwards to Civ 3. We don't even get the tax slider.

Research: No tech trading, a dumbed-down tech tree with very arbitrary connection.

Social policies: Broken right now. I don't think Firaxis patching is enough, modding is required.

Diplomacy: Where are my spies?

Culture: Well, the Civ 4 Religion system was a bit too complex, but they didn't need to trash all of it. Couldn't we get to keep something?

Victory conditions: Doesn't seem to be anything new here. Domination victory conditions seem unnecessarily complex.

Multiplayer: Haven't tried yet.

Other features: I think I included all.
In all, this was 14 major changes that were not to the better. That is disappointing.