As John says, the phone is ridiculously big - massively bigger than the missus' iP6, Apple's equivalent 'small' phone. That's a strange design choice, given it was specifically created because of the dismal failure of last year's barn-door sized N6. Having said that, I've already gotten used to the size after just 2 days.
Like John, I love the fingerprint reader. The placement works really well in every day use, though it is difficult to access when the phone's in a bracket during use as a GPS.
The camera also seems good, though the new app is a tad flakey and kinda spartan - there are absolutely no effects (unless you count the 120fps slo-mo). The videos I've taken have been rather gorgeous, though - way better than anything I got from my N4 (and controversially, I thought the HD video from that was OK). Not sure if the camera is actually better than the one on the missus' iP6, but at least it's comparable - which I don't think could ever be said of a Nexus' camera in the past.
Speed seems fine - despite the miserly 2GB of RAM - and the screen looks really good (again, I'm coming from a 3 year old, middle-of-the-road phone here). I have the 32GB model which means just shy of 25GB free space. Compared with my 16GB N4 that effectively means almost 2.5 times the storage - which seems great to me.
Battery life appears OK (this is only day 3 so hard to be sure), though not spectacular. The snooze function works well and keeps consumption under 5% overnight. Combined with fast charge - which is definitely fast - that means, instead of charging overnight I can pop the phone on the charger when I get up and it's at 100% by the time I leave the house. Which is kinda cool.
Otherwise, Android 6.0 seems a bit meh. There's clearly new stuff under the hood but it's really hard to spot the differences with the latest cut of 5. I eventually found the app access control stuff which is nice to have, though few non-Google apps seem to support it yet. The changes to how USB mode is controlled though, are a PITA as (so far as I've been able to find) you have to manually enable MTP from the status bar each time you connect. The biggest change I've noticed is that I now get an extra column and two rows of icons per screen (which means I now have everything I need on a single screen) compared to my N4 - and I'm sure that's a function of the screen size rather the O/S version.
Reception seem to be on a par with the N4, which means OK but not great.
The main downsides are that it does feel a bit low-rent - particularly compared to the missus' iP6 - and here in the UK, it's really not cheap: the 32GB version I have is £379 which is $583. Bit of a rip-off compared to the US price - if my N4 hadn't been on it's last legs, I probably wouldn't have bought it.
The other big downside is sound quality which is frankly, a bit pants. Particularly on calls - probably the worst call sound I remember having on a phone, at least this century - though it is still perfectly usable. The front-facing speaker is reasonably loud at least - I can even hear it in the car.
Overall, I'm relatively happy with the phone. It's definitely not the bargain the N4 and original N5 phones were, but as a phone, it does seem to do the job. Having said that, I am categorically not a power user so YMMV.