It's great! I'm not saying the device has changed my life but it's a big step up from the OnePlus X. I'll break it down in terms of features.
The camera! Oh my. The flagship feature of this device. It's amazing. I've been taking lots of photos over the last week while on holiday and I've been posting them on Instagram. A couple of my favorites are below.
I've found myself using Google Assistant quite a bit. Setting alarms, reminders, timers, and playing music. I've also used it to identify tracks that are playing. The "offline" identification doesn't seem to really align well with the tracks I've be surrounded by. I'm very interested to try the Google Home Mini that keen Pixel buyers should get for free. Squeezing the phone to enable GA is surprisingly good and the adjustable level of force required is a nice touch.
Stock Android is really really nice. Everything feels buttery. Knowing that I'll get updates for the next 3 years is comforting, especially in a world where Bluetooth and WiFi are broken. Importantly getting the updates means that I'll have a larger set of emoji, so many messages make no sense when half the emoji don't render.
The fingerprint reader is lovely, I know it's a super old feature but I've been really enjoying how fast it works and how intuitively it's positioned. Just picking the phone up and it unlocking magically is just perfect.
Fast charging is amazing. It's really nice to be able to charge it quickly at work or before going out. I hope this means I wont ever accidentally leave it plugged in over night and start ruining the battery life.
On the subject of battery life. I go about a day between charges with a lot of usage. This means nothing, I'll have to see how it performs after a few months.
USB C is a given these days in my opinion. Right now the only devices I use that don't charge with USB C is my kindle and my headphones.
At this point I'm sufficiently impressed to consider buying the Pixel Buds. Last weekend I "Ok Google"ed while walking down the street yesterday and the headphones will help me descend deeper into Google's dystopia. No I don't miss the headphone jack.
Is it worth the £630 price tag? How much is £630 worth to you? Most of the things it does can be accomplished with a far cheaper device. However for a device that I'll use 2-3 years, less than a pound a day for a good experience is acceptable to me.
 You can set GA to use Spotify as a music source which is ideal. However right now you can't get GA to control your Sonos. A tweet from Sonos suggests that they're working on that functionality though. 
 this whole thing sounds absolutely ridiculous for many reasons.