Three? Oh, they must have the Colonization stand alone bundled in there.
I would argue that CIII was the better game, except I expect my Civ games to be multiplayer capable, and CIII failed. As soon as you reached flight, CIII would go out of sync.
CIV (Thats Civ IV) was designed to be Multiplayer first and foremost. While I think it lacks in certain areas, it is by far the best version of Civ out there. (I never played Civ I though, so I can't speak to that one) One of the more annoying aspects was the addition of interesting choices. In Civ III (and II) all you could do to a tile was mine it or irrigate it. Depending on what kind of resource is in the tile, you can do a dozen different things to tiles in CIV, build a cottage (which eventually grows into a town) a Quarry, a Mine, a Lumbermill, a windmill, etc.
Resources matter, not in a way that I like, but they do matter. You need Iron for swordsmen, you need oil for tanks.
For Military, the aspect is experience matters. An Axeman (str 5) beats a Swordsman (str 6) most of the time because the Axeman starts with a +50% vs Melee, while the Swordsman gets a +10% city attack. But, if that Swordsman gets 5 XP. You can give that swordsman two promotions. In particular for this fight, you'll want to go Combat I (+10% strength) and then Shock (+25% against Melee) Turning the fight into an Axeman (7.5) vs a Swordsman (8.1). In theory, a Spearman can still beat a Tank... hehehe... if it were experienced enough.
I think Civ IV could be much better, with a vastly improved resource system, along with a little bit better Combat system, I liked CIII because it was so easy to modify, it didn't require a computer programming degree like it does with CIV. (Although I will give them credit, everything about CIV is wide open, if you have that degree). But given that CIII won't behave in multiplayer, I gotta give CIV the better hand.
Finally to answer your question, is it worth it? There are only three games that I play regularly, SFC:OP, CIV and World of Warcraft. So, I think it is.