So I've had mine for awhile and I can honestly say this is the best phone I've ever owned. I've been on a Windows Phone kick for awhile (920, 925, 1020, 1520) as well as an iPhone 5, HTC One, and an LG OG Pro.
Android, which used to bug the hell out of me, feels very mature and fast (at least with CM). I do miss some things, I liked Blinkfeed on the HTC One and the "people" app on Windows Phones and I believe Cortana is currently better than Google Now. That said, I'm a big fan of the app start-up scene, and getting access to a lot of "non-essential" but awesome apps I did not have before is great.
The phone build quality isn't at the level of Apple, Nokia, or HTC in my opinion, mainly due to material choices but there is nothing "wrong" with is, it just doesn't feel quite as sturdy. More Samsung/LG-ish to me. The camera quality is acceptable (although I constantly miss my 1020 at concerts), the screen is good to excellent, the hardware is fast, and despite its size it fits well in my pocket and hands.
If I could change one irritating thing, it would be the USB connector on the bottom. It seems weak and I have nearly put the cable in upside down a few times because it is flexible. It's a minor quibble but reversible USB can't get here fast enough.