Well, since I mentioned Terry on the last entry, it'd be criminally wrong not to mention his very awesome shooter :). This is a bare bones game, wave after wave of enemy coming towards you at breakneck speeds with you having only one life. The question being: how much of this can you bare in 1 session? :)
P.S. Give "Pathways" a go, at least if you like a bit of experimental gameplay. Also, check out his first commercial game, VVVVVV - there's a free demo on his website.