When I first played Pandemic I was enthralled by the level of intensity in this co-operative board game. We felt like there was so much at stake in the game, we were constantly on the edge of losing control and really had to work together and communicate well to win. Also, winning can be difficult in this board game, which adds to the interest and 'addiction factor', at least at first.
This is one board game where I would *absolutely* recommend the expansion, 'On The Brink'. The game does get a little stale without it, but the expansion provides another level of difficulty and unpredictability.
One thing to watch out for in this game is an overly-dominating personality in one of your fellow players. The only bad games I've ever had are those where one person is just telling everyone else what to do - this sucks all the co-operation and fun out of the game quickly. Play with a good group and you will love Pandemic.