I have a big problem with Civ5, which is why I cannot say that it is better than Civ4: All of the little things that made the prior games fun are not in this game.
In my opinion:
- The battles feel somewhat flat - I don't think the death stacks of Civ IV are the answer, but I don't think forced one-unit-per-tile is it either. The mechanic of sitting outside a city with siege units, shelling, and then moving in with units is pretty boring. The re-introduction of ranged attacks did not fit well into this game. It's also pretty awkward when each ranged attack does 1 damage, so technically 10 archers could destroy a tank column.
- Barbarians? Just awful - Where's the ship-to-land invasions? Where's the brutal barbarian hordes trying to sack my capital? They actually can't even take over cities - it's pretty lame. There's a barbarian mod that puts a band-aid on this boo-boo in the game, but I feel that that modder's hands were tied because the barbarians are so bad to begin with. Historically, barbarians weren't just in encampments - they were whole civilizations! I liked Civ4's barbarians much better. Civ II's were also good.
- I preferred transports to units just jumping into the water to invade. This is pretty terrible. It makes invading by sea so awkward when all of the units are slamming into each other. Swimming units are also very hard to protect when you've got a bunch of them moving over the ocean.
- The AI is a joke in war. If you're on an isolated continent, you could be still in the stone age and they will never send units across the ocean to attack. Land AI is much better, but the AI does stupid things that gets itself killed. They will jump into the ocean when you have a trireme right there. They will sit their great general out in the open so that you can just pick it off.
- Diplomacy is terrible. None of the AI have unique personalities. They will pretty much hate you for any little thing. Even Gandhi will launch a preemptive strike on you.
- The SDK map editor is really bad, and should have really been included in the game as a world builder. It's tedious at best. Why do I have to create a project, build it like I would compile a program, and then start the game to play it when I could just build that in-game with a world builder and save it? Thankfully, there's a mod out now that's almost as good as Civ4's World Builder (It's called In-Game Editor - a very good mod!)
- After your riflemen become antiquated (as the game approaches modern times), warfare just isn't fun anymore. I would actually even say it becomes somewhat boring. I think this is because of one-unit-per-tile. It becomes strange where you can only have infantry in one hex, and tanks in another.
- Dozens of other, small things that make you want to come back to the game, like for example having an accurate earth map among other good scenarios, good GUI, good sounds and effects, minimal noticeable glitches (Civ5 is absolutely loaded with them), a good 'flow' to the game, etc.
Overall, Civ5 is a good game, but will never be great like Civ4. There's too many holes or tedious elements of the game play to make it as fun. I would give Civ5 a 8.5/10. and Civ4 a 9.5/10. In my opinion, Civ5 was never finished. This becomes apparent just by playing the game a little bit. It doesn't feel polished in the least bit.
I love the music of Civ5, though. It's better than Civ4, though I somewhat preferred the period pieces.