1. I haven't found a pair of in ear decent headphone, that pairs good whith the 6P I've used some samsung ones, htc ones and even lg... The pouse/play/skip vol up and down dont work.
2. Split screen or multi window or whatever you call it would have comed in handy whith a great big screen that the Nexus packs
3. Miracasting, or screen miroring does not work whitout chromecast, whitch is a total lie, I used my ex SGS5 no problem, my ex LGG3 did a awesome job at it whit my samsung smarttv, music, movies games internet everiting worked wonderfully, qhith the nexus some YouTube, but not quite.
4. Another downside is probably the best feature of a nexus device, the latest operating sistem,bother producers spent more time tweaking it to work flawlessly, the nexus is also do not forget, permanently testing the newest android version... some google play aps have yet o get optimization, etc
5. The service/repaire policy provided by google and/or huawei is notoriously bad, overpriced and sometimes imposible to get. A good example was the shattering lens protector thinggy ...glass (many said its a design defect although I like it, but is incredible fragile), first they refused to acnolage the problem, second they refused to warranty it, a cheap small piece of glass was for some time 50$ for just the part + labor, so yeah it cant be repaired in a decent profesinal way.
It was 2015 best all-round device and still the best option on the market, but its far from perfect, some downside of it only became noticeble over time, expecialy if you needed service or repairs (the whole affair just makes you think of those things for your next device) so yeah take care and be carefull whith your nexus, maybe put some protection and/or some insurance on it. It will come in handy if you ever need it...belive me.