Well, I've recently bought Humble Bundle 8 and almost all games included fit the bill:
- Dear Esther. It doesn't really have anything you could call "gameplay", but it's a nice, short and beautiful experience.
- Proteus. Another one that doesn't really have any "gameplay", except this one doesn't even have a story. It's strange, I personally can't say I like it, but it did get some positieve reviews.
- Thomas Was Alone. Has already been mentioned.
- Hotline Miami. One of the most violent, trippy and interesting games I've played in quite a while. A messed up story with solid gameplay delivered with retro graphics and a mind-melting soundtra- Oh. Wait. You already played that one, never mind.
- English Country Tune. A series of puzzles with different mechanics. Old school fun that has its challenging moments.
- Little Inferno. Has already been mentioned.
- There's also Awesomenauts, Capsized, Oil Rush, Intrusion 2 and Tiny and Big in Grandpa's Leftovers - but I have yet to play them.
If you haven't bought it already, I sincerely recommend it (even if you have Hotline Miami already). You can pay whatever you want - though I suggest paying more than the average $5.84, because then you get 11 games instead of 5. You've still got one day and 10 hours to make up your mind.