Well, Portal technically has a gun and is first person, and one of the best game ever made 
Out of the 'real' shooter games, I'd pick Bioshock, with Half-Life 2 a VERY close second. I know Half-Life is technically the better shooter (shooting in Bioshock was boring and poorly done), but I thought the Plasmids were a great idea (what other shooter allows you to fling HORNETS at your enemy?) and the overall story and setting of Bioshock appealed to more then HL's.
Modern Warfare is a honorable mention for it's incredible atmosphere, but I generally don't like games set in real-world wars. It just feels boring und unimaginative to me.
Out of the 'real' shooter games, I'd pick Bioshock, with Half-Life 2 a VERY close second. I know Half-Life is technically the better shooter (shooting in Bioshock was boring and poorly done), but I thought the Plasmids were a great idea (what other shooter allows you to fling HORNETS at your enemy?) and the overall story and setting of Bioshock appealed to more then HL's.
Modern Warfare is a honorable mention for it's incredible atmosphere, but I generally don't like games set in real-world wars. It just feels boring und unimaginative to me.