I picked up Civ IV late and got it for like $3.50 for the 4-pack: vanilla, Warlords, BTS, and Colonization. Colonization is probably good, but really hard to get into because it only makes you want to play BTS or FFH. Very fun.
Here's my list of minor issues with Civ V so far:
- Bonus resources are underpowered. They each need their own unique little bonus besides just +1 food/production. Bananas you should be able to plantation without having to clear the jungle, for example. Sheep should give like +1 happiness. Deer should give +1 happiness without even having to work it. Stone should do the same thing it did in Civ IV: speed up the production of certain wonders.
- Bismarck should get a bonus to maximum supportable units. Their bonus to recruit barbarians is nice, but it's useless if you bump into the supply cap.
- It needs to be more obvious that a city of yours is not just in your trade network, but also railroaded. It's hard to even tell the difference.
- City states are too expensive early game. Maritime city-states are not too useful when playing OCC.
- The wonders are a little bit dull--which would be okay, if there were more of them. Need more. The Pyramids might be the one exception, since they can cause you to actually have too many workers.
- Discovering the world is round in Civ IV was cool. I wish it stayed in.
- Great Engineers good, Great Scientists good. Great Generals and Artists...not so much. Can't you let the Generals and Artists bulb certain structures instead of the Engineers? Let the Artist bulb Sistine Chapel and Hagia Sophia, for example. Let the Generals bulb Heroic Epic or the Kremlin.