The promotion really applies to two bundles: the Xbox One Assassin's Creed Unity Bundle with Kinect, and the same offering sans Kinect. Normally these boxes sell for $500 and $450, respectively, though today the bundle with Kinect is marked down to $450 and the bundle without Kinect costs $350.
Both packages already come with a pair of downloadable titles -- Assassin's Creed Unity and Assassin's Creed IV: Black Flag -- plus a wireless controller, chat headset, and of course the Xbox One console itself with built-in 500GB hard drive.
As part of the 12 Days of Deal promotion, you can also select a free game from a selection of nearly two dozen titles. Some of the highlights include Grand Theft Auto V (see our review), Forza Horizon 2, Call of Duty: Advanced Warfare, Halo: The Master Chief Collection, Dragon Age: Inquisition, Wolfenstein: The New Order, and The Evil Within, to name just a sample. There's also more family friendly fare, like Lego Batman 3: Beyond Gotham, Terraria, Monopoly Family Fun Pack, Plants vs. Zombies: Garden Warfare, and so forth.
The free titles range in price from $30 to $60. Combined with the $50 discount for the Xbox Bundle, you're looking at a savings of $80 to $110, and that doesn't include the two Assassin's Creed downloads. In other words, this is a good deal, folks.
You can shop the discounted bundles in Microsoft's online store.