Carries the Civ franchise mantle with competence.
The big development in terms of combat is the elimination of unit stacking. I found this this hardest part of 5 to get used to and while it didn't turn me off totally at first, was something I thought was a step back. After several 100s of hours of play though it seems to me now that there's something to be said for both configurations. The stacked combat had the potential to become monotonous, especially at later stages of the game when civs would have flush and developed armies. Unless you disabled combat animation (and wheres' the fun in that!), a stack of 30 or so units could take a long time to resolve. On the other hand there was something satisfying about bludgeoning a city with a massive strike force all at once. And while the single unit approach is undoubtedly more realistic in some ways, even after much play getting units into position to attack can be frustrating and awkward, especially given the much more palpable terrain penalties of 5.
The addition of ranged combat in 5 is really nice. This was a definite lacuna (with the Mechs of BTS being a possible exception) in 4. Ranged combat also offsets somewhat some of the advantages of the stacked combat protocol in addition to giving siege warfare a more realistic feel.
The other thing I really like about 5 over 4 was the decision to get rid of some of the less captivating city stats, like health/pollution. City management is more streamlined in 5, although the specialist placement can still be mind boggling, even to a veteran player.
The Giant Death Robot lacks creativity and I miss the Dreadnought and Cyborgs from BTS. I hope later expansions bring back something comparable. I also liked the Navy Seal unit which it was sad to see go. Some of the new unit additions are pretty dull and some civs seem to really have an up when it comes to specialized units compared to others. Others tend to be early game specific. I understand this makes historical sense but still... Of course, the US again probably has the best two special units with the B-52 and the Minuteman with Germany coming in 2d with the landskneckt panzer combo. France has a nice combo as well. England's special units are positively boring. I don't play some of the civs just because their special units are so uninspiring relative to the others.
The AI's are good, but the level setting I think suffer from the same lack of gradation as in 4. It seems like in both everything up to prince is fun and challenging but the minute you try for King or its 4 equivalent, it goes from hard to impossible.