Do keep an eye on the Following Freeware articles. They are a mixture of online and download free games and I've already got an interesting looking list for December.
If horror is your sort of thing (Dark Visions had horror overtones from what I played of it) then
Exmortis and its sequels may well be worth a look.
If you'd like something completely the other way (bright and a little bit silly, but no less brain-taxing for that) then
The Dreamerz could be a good bet.
Otherwise give some indications of your preferences and I'm sure we can find something for them.
