Fingers crossed, but in 7 days time when I am playing Space Marine...I might have a new near top of my list game
It is kind of bandwagony, but HL is one of the greatest series of games ever...and it spawned soooooooooooooooo many awesome mods (CS my favourite).
In terms of a single game, its always hard to choose, but Dungeon Keeper/2 always come close to the top of my list (and as a series too ofc), as well as Giants: Citizen Kabuto.
Fingers crossed, but in 7 days time when I am playing Space Marine...I might have a new near top of my list game