I always preferred the 'Unreal' game to 'Quake', especially multiplayer. My favourite games though are the RTS games like Red Alert and StarCraft.
Unreal 2003 is quite good but not the quantum leap forward it was hyped up to be - just more of the same but a bit sharper.
I remember playing a game years and years ago called 'Return to Zork' where I got bored and shot dead an innocent postmaster - that played on my mind afterwards.
I shoot scum and aliens all day long on the computer but in real life I wouldn't hurt a fly (literally).
Just remember - it's only pixels!