I got chance to use this phone for 13 days.
I it was running on windowa 8.1 with denim for first
6 days and I installed windows 10 build priview for next 7 days.
It was smooth on windows 8.1 and ram mangement was also good until you run heavy apps and games,
I played games like asphalt 8 on default graphics. Few frames dropped got stuck for a couple of seconds but it did not heat up. Display quality is adiquate.
The battery drained a bit faster for handling the game. it was playable for most part. Camera performance was slightly above average in ample lighting it sufferd from dark conditions. Front camera was ok, video was also
ok but not still. It was smooth in regular usage. Call and signal reception is good speaker is loud.
Windows 10 bought some new features as it a developer preview it has a lot of bugs.One thing I noticed that in both versons of windows while charging if u used it its unusable the display became very sensitive, even the slight touch opens unwanted settings and all othe files when I pressed and holded back button for multitasking it just went back to home not uasble.same gose for gaming multi touch was not good.cortana worked fine over all it handeled windows 8.1 fine ignoring touch response.