I would strongly advise you to get the base game and all expansions.
Be advised though, the 3rd expansion called Shadows is now in beta. There hasn't been any definitive information about a possible bundle, but when it comes out it might cause the game and previous expansions to go on sale.
The expansions really made the game much better and more fun.
Laptop: Intel Core i5-2430M 2.4Ghz, Nvidia GTX520M, 8GB RAM, Win 7 64bit
Desktop: Intel i5 4670K 3.4Ghz, Nvidia GTX780, 16GB RAM, Win 10 64bit