Half-life is not the best game ever. It's isn't even the best FPS ever. It's arguably the best game of 1998, but if you ask me even that is pushing it.
Edit:
Half-Life is not the best game of 1998, gaming press be damned.
Starcraft
Total Annihilation
Rainbow Six
Thief
Grim Fandango
Fallout 2
Baldur's Gate
These are all 1998 PC games.
Plus, Unreal is also a 1998 game and its graphics kicked the pants off Half-Life's graphics