I know many people hate the series now, but Call of Duty 1 or 2 or COD4 Modern Warfare were good games IMO. After COD4 though, the series just became one derivative sequel after another.
I would also suggest Fear 1 and the Half Life series. Borderlands 1 was great, and I am currently playing BL2 and enjoying it, but it is not really a serious shooter, more of a humorous sci-fi shooter.