i'm a big fan of cheap software, and regularly scan the $9.99 bargain bin at the Evil Empire (wal-mart) for cheap games that can run on my ancient low-end computer.
naturally, ive had mixed results, and your mileage may vary.
Pool of Radiance, FRPG - you lead a party of the usual demihumans and root out evil with swords and magics. poor. where were the playtesters? careful adherence to AD&D rules results in a nearly unplayable game. up ahead you see orcs! you direct your meat shields (on their turn) to advance and attack, while your rangers and mages hang back. your fighters run right past the bad guys, which fall on your mages and rangers. graphics are good, and the storyline too, but has anyone actually bothered to finish it?
Conflict Desert Storm, FPS - you lead a SpecOps team and root out evil iraqis with m16s and sniper rifles. good. modern weapon tech, drivable vehicles, zoomable 1st/3rd person perspective, superb graphics for my low-end card, very playable, lots of varied scenarios let you play to your strengths.
SWAT, um, 4?, FPS - you lead a swat team and root out evil drug dealers and gun-runners with guns and flashbangs. bad, probably my fault. died dozens of times at first contact, usually didnt even see what got me. i gave up. pretty, but who wants to die prettily again and again and again and....
Dungeon Siege, FRPG - you lead (or go solo) demihumans to root out the evil demon gom with swords and magics. very good. spectacular graphics, very easy interface, good storyline and music. actually tried this one as a multiplayer on the lan, still fun.
Marine Sharpshooter. FPS - lead your spotter and root out evil terrorists with your sniper rifle, duh. meh. requires a scroll mouse to use the scope, got shelved. looked ok, may get back to it.
Black Hawk Down. FPS - lead your squad and root out evil somali militia with 50 caliber machine guns, m16s, satchel charges, AT4s. very good. interface is usable, music good, graphics good, lots of varied scenarios. you cant drive the humvees or choppers but you can shoot the miniguns, and die in them. awesome weapon that it is, i would not want to man a 50 cal from the top of a humvee. i want both feet on the ground, and my squad covering my back. the bad guys shoot at you from behind trees, windows, rooftops, speeding pickups. im getting killed regularly, but something keeps me coming back for more. and i'm learning. move slow, use cover, dont waste ammo, see ahead and live. charge ahead and you die.
Oooh, Undying - What a helluva game. Others to keep an eye out for are Fallout 1 and 2, and Planescape: Torment. These three games are probably three of the best RPG games of all time.
I Loved the "Loooooook"..."Scryeeeeeeeee" whispering stuff. Also, they put in some very neat, subtley-scary creepy scenes in there, like when you are wandering around, through the vally, and those creatures are running on either side of you, you see "hints" of them, evey now and then...
There were a few cenes in "Nocturne" that were like that.