While the expansions do have a ton of stuff to offer, the original game has been updated and revised so what is on the shelf to buy is still a great purchase.
Every game is completely different and that's why I love it. Yer strategy has to change every time you play it. It caters to tons of table talk, alliances, double crosses, border disputes, resource grabs, and general shenanigans.
With 5-6 players, we averaged games lasting 6-8 hours (after setup); with one lasting 12 hours.
I highly recommended it to anyone who wants to piss off their friends for a week or two. =P