One of the things that really sucked about Steam was the inability to get refunds on certain purchases. Services like GoG and Origin had it. Well, that changes today as Steam has a new refund policy in place.
If you've played the game less then two hours and it's within a 14 day window, you can request a refund for any reason. That's not a bad policy and should help alleviate some of the headaches when purchasing a game and seeing it not work on your system. For those that pre-purchase games, you can ask for a refund anytime before the release and then within the 14 day, two hour play limit. DLC has a 48 hour time window and there are a few things Valve can't offer refunds on.
You can also return a game and repurchase it if the game is on sale and within the 14 day, 2 hour time frame.
Of course, measures are in place to try and make sure people don't abuse this new policy. From the looks of it, I think the system has some nice ground rules and is a long overdue feature that should make many folks happy.