I'm not sure I'd go with Half Life 2 myself, a lot of the best mods for it are multiplayer centred and as the rules go, you can't really play them, so unless I wanted to play against bots forever, I'd probably have to say no. Plus there is the size of the mods as well, they'd take ages download on the crappy connection the island has.

Still thinking about my own choice though, I'm narrowing down the list, still.