Free games are always exciting news, and now we know what games to expect from December's Xbox Games with Gold offering. Some of the games are not available for the full month, but all of them will be free at some point in December.
On Xbox One, you'll be able to grab Warhammer: End Times - Vermintide any time from the start to end of December. Telltale's Back to the Future: The Game - 30th Anniversary Edition will be available starting December 16th, and will stay free until January 15th 2018.
In terms of Xbox 360 games, Child of Eden will be free from December 1st until the 15th, with Marlow Briggs and the Mask of the Death available the later half of the month from the 16th until the 31st. Both games will support backwards compatibility on the Xbox One, so claim them for free and you can play them on that shinier new box too.
Basically, log in on the 1st and 16th of December, and you should be able to grab all of December's free games. They're free, so why the heck not grab them?