There are some good things:
- 1 UPT is a nice improvement in military strategy. Much more fun than stacking.
- Hexagons have a nicer look than squares.
- City-states are a cool feature.
- I like being able to "embark" units on the sea without having to build a ship for them.
- Social policies are a cool feature that provide more options and long-term planning than civics.
- Leaderhead graphics look very impressive.
- Strategic resources now allow only a limited amount of units, making them more important (at least in the early game, later on it doesn't seem to matter much anymore).
Those are the things I can say are definite improvements in Civ V over Civ IV. Not all of these things were perfectly implemented, but I believe they can be fixed and improved with patches.