Steam is finally getting a proper refund system. Starting today, users of Valve's PC platform will be able to get a full refund on any game for any reason, provided it's been less than 14 days since purchase and they have spent less than two hours playing.
You'll be able to get your money back for DLC, bundles, and even pre-purchased games with this new system, which will make pre-orders feel like way less of a risk. (Once a pre-purchased game is out, Valve says the standard refund restrictions will apply.)
You can also get refunds on Steam Wallet funds, although they won't be available for gifts, movies, or games purchased outside of Steam and used on the platform.
Also worth noting, via Valve's FAQ:
Refunds are designed to remove the risk from purchasing titles on Steam — not as a way to get free games. If it appears to us that you are abusing refunds, we may stop offering them to you. We do not consider it abuse to request a refund on a title that was purchased just before a sale and then immediately rebuying that title for the sale price.