My [early] thoughts on the Xbone - 3 days in..
The interface
It could still use a little refinement and it will probably evolve over the next few years but already it's far better than the current 360 interface. It DOES take a little getting used to since they've re-organised a lot of stuff. The basic features are pretty much all thier own apps now, it's fairly compartmentalised but it's quick and easy to move between them all.
I quite like being able to scan a QR code with the Kinect rather than typing in a 25 digit serial number - and there's no chance of typos.
Avatars carry over from 360 but there really isn't a place for them currently, I don't think they'll be missed if they are phased out.
Now that I've got my bearings a bit, I find I can get around pretty quickly using voice commands.
the video / entertainment apps are decent - sort of more of the same - but it's pretty handy to be able to list them as channels in the tv guide - i've not used that for TV actual yet, though.
Overall there's a lot less clutter and it's a lot more fluid. There is still a bit of loading some of the time but it's not like the headache of the NXE on 360 hardware - almost constant loading / waiting.
You can message people and see their details across the 360 - ONE divide but you cannot party / chat which sucks a little.
The audio quality in general seems much better with voice chat - both with Kinect and Headset.
The games
In getting rid of the DRM 'features' that upset [just about] everyone they also got rid of the useful feature of only needing the disc to install a game. This is where the system falls down a bit. Take Forza 5 for example - after a lengthy install that filled up 33GB of my 500gb hard drive - The game wanted a 6GB update - ON LAUNCH DAY - and I still need to have the disc in the tray when I want to play it. Kind of a worst of both worlds approach.
No more racing home and popping in a game right away - it's put a disc in and go have dinner while it does its thing.
Forza is a lot of fun though. I also picked up Battlefield 4 and Assassin's Creed 4. Both are good fun and look great. I fell out of love with Assassin's Creed early on with the repetitive nature of things but I'm quite enjoying part 4 [I'm pretty sure there's quite a few more than 4 of them already?]
Overall
It really is a system that's designed to go hand in hand with internet access and if you don't have decent broadband you probably aren't going to have a great time.
As an entertainment hub it works great but the system really needs MORE games and apps asap.
oh, and Killer Instinct suuuuuuuuuuuuuuuuuuuuucks.