My only experience with the game is the solo aspect.  From a solo standpoint the game is probably the best shooter/crawler ever but to linear for me.  I like a more open, sandbox type game.  Half-Life took an already crounded genre, refined and did it better than anybody before or really since.  Flawless game play, easy and intuitive controls and top notch story line.  I think the story was the best part of the game.  Despite my personal views this really is a must have for any pc gamer as it really is the top game in its field.