I'm really hooked on the game Strange Adventures in Infinite Space by Digital Eel. The best way to describe it is to say that it's a cross between Spaceward Ho! and the classic Super Star Trek, but… enhanced... so that the entire play experience takes only 15 minutes. This is a great game to play while you're waiting for a download, boiling water, watching paint dry, etc.
You play for a literal high score, which is something you don't often see in modern games. To get the best score, you must explore a game space that is filled with lots of discoverable ship upgrades and loot that you must return to your home planet. But since there is no reference guide of any kind included with the game, you might want to have a notepad handy so you can remember which ship upgrades and loot are the best to keep.
Ernest Adams has a more detailed review where he calls SAIS a "perfect short game." For a mere $15, I'd tend to agree. Now I can't wait for the sequel, Weird Worlds: Return to Infinite Space, which should be released this month.
Update: In a way, SAIS does include a reference guide of all items in the game. All of the data for the game is stored in simple text files in the installed
gamedata directory. Of course, reading it is a little like cheating, and does take away from some of the discovery. The data is so easy to modify that Digital Eel even includes a mod guide and a graphics packing tool. I sure am impressed with the elegance of both the game design and its architecture. Inspiring stuff for old game hackers like me.