because 3 of 5 games listed are out, and ive played them, i'ld have to say ut was the best, just for the staying power... it was also the only one with multiplayer. painkiller reminded me more of serious sam (which is a bad thing because i played that game for ages) and far cry gameplay was mediocre( the graphics however were stunning) and ut2004 i believe was a good balance of dm and tactical gameplay with excellent physics and graphics.
based on reputation; doom 3 and half life will own all of them... I just can't vote for them yet as i havn't played either.