Just wanted to say that I tested this out yesterday morning. For the first time, I am impressed with the XB1 without reservation. I got invited into the preview they day prior by a friend when this was announced. I'd never had any desire to be in the preview program prior. Within 24hrs I got the message from XBL, downloaded the update, and was rolling.
I wasn't sure how to go about finding/trying the preliminary preview of the backwards compatability. I couldn't find it, so I was thinking "meh, overrated".
I went into my games library to re-download Guacamelee so I could do the new achievements in the next couple days. What did I see right there amongst all my Xbox One games? I saw 360 games that I have downloaded on my account before that are part of the initial batch of games. Clicked on Banjo Kazooie, Nuts and Bolts, downloaded it, and started playing. Impressions:
1. Load times are definitely faster than they were on the 360. I still had my retail disk of Nuts and Bolts so I turned on my 360 and tested them out side-by-side, and the XB1 definitely loaded it faster from the digital copy than my 360 could (and it is installed on the hard drive on the 360, if you're wondering). I tested it against the digital download of N&B too since that was a games with gold at one point I think (either that or I bought it digital on sale at some point, b/c it's in my digital purchase history). Even from the digital-only version, the 360 was still slower to load it than the XB1. So however this emulation/repackaging/recompiling/whatever-the-hell-it-is works, it works really well.
2. Image seemed a little crisper. Obviously they didn't uprez it or anything, but it just seemed ever-so-slightly sharper on my XB1 than on the 360. Maybe just a better HDMI signal through the XB1's beefier HDMI cable. I honestly don't know, but I could see a difference. It was akin to the difference between going from 1080i to 1080p, although obviously this isn't a 1080p game.
3. Very convenient to just have my digital 360 games right there in my XB1 digital games library.
If they can get even half of all the games (both retail and XBLA) into this program, it is definitely a massive value-add to the XB1 and will probably convince me to finally get rid of my 360.
I would hope that games that only have Kinect support but don't use it in any real meaningful way are still eligible for backwards compatibility, like Mass Effect 3.
This is exactly how it works. As long as the game isn't Kinect-required, but rather simply Kinect-enabled, it would simply play the same way it does on any 360 without a Kinect hooked up.