I reckon
FEAR
S.T.A.L.K.E.R
BF2142
ArmA
Graw
HOWEVER the first 3 are entirely dependant on your prefered game playing style;
FEAR is a gritty, horror-inspired, fairly tight on the rails level-design shooter,
STALKER is a fairly open post-apocalyptic Russia, modern-day, oblivion-style title with some thrown in anomalies, mutants and other wierdness (Im enjoying it more than I did Oblivion though, despite Oblivion being in my favourite genres - fantasy and RPG, and larger) and has a slight RPG bent in the way the armour and weapons work, despite being an fps, whilst BF is and always has been a primarily multiplayer experience, best savoured in a group with a few of your mates.