Really? Are you fucking serious? Anyway...
1.DA:O > if you really like it, go for NWN, BG2, FO1&2...Planescape for extra credits:P
2.Bioshock > -//- Sistem Shock 2 & Deus Ex.
3.Morrowind/Oblivion and/or FO3.
4.Rome:TW and/or Medieval2, Shogun, Napoleon.
5.PvZ.PvZ.PvZ.