I would recommend to see if you can run any of the early Splinter Cell, Rainbow Six, Call of Duty/Medal of Honor series. Half-Life 1 you might be able to run, don't know, if you like it there's 2 or 3 addons that continue the story.
serious sam is a nice fps, but very Quakey in terms of point and shoot.
I believe there was old delta force series (i'm not sure of the exact title) I remember a distinguishing feature in that game was that every time you fired you would see a straight line between your gun and point of impact.
as far as tactical/military games, this one isn't an fps, but I've found it to be very realistic and open ended: Jagged Alliance 1/2/2.5