Civilization 5 is one of those games that kept me up until the next morning every time I started playing it. How do the predecessors hold up?

Civ 4 is rather underrated. It did some new things and spiced up the civ formula. For this price in this bundle it is totally worth it for the game and the expansions.

Civilization IV is considered by many long-time players the pinnacle of the series. It has a brilliant design and a miriad of mods that add even more value to an already masterful game

Sure. My impression is that Civ IV is the favourite of the fans along with the slightly forgotten Civ II MGE. So probably the term underrated fits better in titles like Civ I and III.