Did anyone find out last time if you got to find out what it was before deciding to keep it or gift it to someone else?
I don't know if you found out before the purchase was completed, but you can purchase as a gift and if you want to keep it just redeem the gift code yourself.
Also, I believe that if you made such a purchase and decided your didn't want the game and preferred to gift it, customer service was pretty good about doing the work to remove the game from your library and issue a gift code.
Update - I hadn't thought of this drawback to opting for a gift code:
Public Service Announcement: Be warned, if you buy the Mystery Game as a gift, there is no guarantee that you won't get a game you already own. This has been standard practice in GOG sales for a while now. Basically the computer picks the game at time of purchase, and when you buy a gift code, it assumes that anything goes.
When not buying a gift code, GOG will filter out games that are already in your library (I guess).
Also, this forum thread has a list of games being offered in the "Mystery Game" purchase: http://www.gog.com/f..._mystery_games/page1