Pandemic is brilliant, its such an incredible design because games are always tight. I didn't go for any of the expansions, but rather picked up Pandemic Legacy Season 1. That way, I won't have played Pandemic too many times before playing Legacy. I might go for the expansions later. Oh yeah, I'm currently deciding if I should wait till my kids are old enough to play with me. They're 5 and 3 at the moment.
But if you're after the expansions, On the brink makes it harder (legendary difficulty) as it adds another disease and 5th player option. In the lab adds another step to the game where you have to produce the cure, and give you more stuff to think about. If I'm not mistaken, Rising Tide, Iberia and Fall of Rome are standalones which follow the Pandemic formula, but adds a new theme and new rules. There's also The Cure and the expansion Experimental meds which are Pandemic dice games.
