Drakan was one of the games supplied for free when I bought a 500Mhz P3 some time ago, and it helped shape my future.
The modding community of Drakan was extremely interwoven with the gaming community, as it is for many community's with such a tight community, everyone would know the progress of each others levels, and many excellent Single and Multiplayer levels were produced in the time I was playing it. Despite having such a small community, someone somewhere was always up for playing against you.
Drakan was the first game that I ever played on the internet, from then I've always been more involved with on-line games, and I'll be hard pushed to buy a game with "an OK single player mode" unless it kicks out some brilliant multiplayer action. Without Drakan I don't believe I'd have chosen my degree in computer games development, and I owe it so much.