Grim Fandango is playable with just one hand on the numpad. I remember Civilization working great with keyboard-only interfacing.
Wow, that’s a gem.
Also, Yarr for the win to you guys who suggested pirates.
Forsaken.
Not a serious suggestion, but it is the last FPS I completed keyboard-only. If you can play piano, you should be in good shape for the multiple simultaneous keypresses required!