I think you can get Civ III Gold for like 10 Euro, so just go get it. And besides get both games they are great.
I personally prefer Civ IV, but it is not without problems.
Civ IV Pros:
- Corruption gone (all cities are productive), replaced by maintance (slows expansion untill you can sustain your economy i.e. it is important to understand how your empires economy works in Civ IV) anyway I look at this, it is a good thing.
- Unit promotions, specialized units make it more interesting interms of warfare
- Because you get fewer cities, you need to adapt to the terrain, no more mindless city cramming into as tight a space as possible. You need to know what city you want and where it has to be.
- More tarrain improvements
- City specialization - good thing imho
- Riots are gone, the effect of angry citizens is now more subtle, crippling your economy and production as a whole, instead of icapacitating your city outright.
- Collateral damage is back, easier to kill SoDs, initiative is important, whoever strikes first has a better chance to win.
- Graphics
Civ IV Cons:
- A/D/M values for units are gone, replaced by Strength + Bonuses/Movement. I think Civ III system is better allowing for more diverese units with particular strengths and weekneses more apparent. i.e. Cavalry in Civ III good at attack poor on defense, in Civ IV it practically doesn't matter.
- Navy is next to uselless, going up against a civ with powerfull navy is no problem, can't do anything except pillage that lonelly fish boat. In Civ III you could destroy improvements up to 2 squares inland really putting a dent in the economy.
- Artilery (a suicide unit in Civ IV) can't cause damage without going into a direct combat.
- Airforce is rather passive
- Alot of modern game doesn't exist, including the airforce, because the game is usually won or lost by that time. Hopefully BtS expansion will fix that.
- Game speed too fast, units going obsolete too fast, don't get to be in particular age for too long, instead you just rush through it.
- Several uselless tiles (mountains/deserts)
Civ IV is still improving though, so it is too early to say for sure