I loved both of them I have to say, however, that starcraft was definately better for me.

Starcraft had a more complete and compelling storyline that reeled you in hook line and sinker and left you wanting more, much, much more, where as Half-Life's story was really just a big mystery, you were given next to no information about the situation and were sort of left to figure out what was going on, which is all well and good except that the game never really gave closure, you never really cared about any of the characters or what was to become of them.

Multiplayer for me, this is probably personal opinion for most people, but I loved the competitive, strategic gameplay that starcraft offered, every game was a learning experience whether it was a win or a loss, and i'm a sucker for good RTS's. Counter strike was and is a great game and i've played it on and off for roughly 5-6 years, very easy to get in to, but its still twitch gaming unless you are playing clan matches, which i admit are immensley fun.

Both excellent games, but Starcraft wins IMO.