Any suggestions?

Can't help with the Linux but I can bump the topic. Also, more descriptive topic's name might help.

People seem to like Super hexagon.

Also Secret of the Magic Crystals. Not much to choose really. See for yourself the titles availables.

Wanted to suggest Escape Goat or World of Goo, but you have them both. :)

I wanted to suggest VVVVVV, but you already have it. I wanted to suggest something else, but it seems you already have all games I'd advise getting that have Linux versions. :P

TF2 for free.