I bought Civ V, and to be honest - I'm regretting it. Civ IV just feels like the better game.
I can understand where you're coming from. It seems the devs had a tough time programming the A.I. to handle one-unit-per-tile effectively, and to compensate players were nerfed and the A.I. was massively buffed. I haven't played for a few months, but I understand there have been some recent patches that improve the A.I. and address some of the other issues.
Never played Civ4 multiplayer, but I had a chance to play some Civ5 one-on-one games with friends and family members and it was a lot of fun. I really like the concept of one-unit-per-tile; however, maybe it was a bit too ambitious.
I grew up playing the original Sid Meier's Civilization and Masters of Orion, and years later I discovered Civ4 and played the heck out of that game. I've probably played Civ5 for a few hundred hours since launch, and so far I haven't gone back to Civ4 yet.
EDIT: here is a great article describing a mod called "Civilization NIGHTS" - which attempts to fix the AI problems with Civ5. Has anyone else tried this one?
http://www.rockpapershotgun.com/2011/09/09/mods-and-ends-civilization-v-nights/#more-73124
Some highlights:
- It would be bold and incorrect to say that Civilisation NiGHTS eliminates all the problems with the AI but it does a damn good job. While there are still issues, over an entire game I find opponents to be more unpredictable, more difficult to box in and more believable.
- There are seven branches now and over a 100 policies to choose from. Although you have to start from the bottom of each branch, they’re all open and picking one will never lock off another.
- Each tree unlocks 2-3 Governments at various points, and as you get further down each tree, they unlock special synergy abilities that boost a variety of buildings from the Renaissance Era onwards. This is to ensure that as you progress through the game, buildings in later eras feel powerful compared to their early era counterparts.
- In the mod, citizens actually generate happiness. Expansion and militarisation take it away again.
Download link and installation instructions: http://forums.civfanatics.com/showthread.php?t=399510