OK I've been using my N5 only since last night, but already I have a ton of impressions. This is a super impressive phone for $349/399. Anyone who thinks this is a 'bad' phone for the price needs to get their head checked -- it's mainly because it does so many things right that it's easy to pick nits with it - there's a ton of imperfections, but overall it's so overwhelmingly positive.
Good:
-Phone feels nice in the hand. Soft touch back feels great, just like on the N7. It's much more grippy than the back on my Galaxy S3, which is like holding an eel. Yeah, the Nexus 5's soft touch back will show grease -- if you plan on using your phone with disgusting greasy hands, get a case or cover for it!!
-Screen is beautiful, text is razor sharp! Color calibration is neutral (unlike my uber blue/saturated Galaxy S3). Very readable in high and low light. Can appear a tiny bit washed out in certain light settings, but it's so crisp and clear I'd take this over AMOLED anyday. Blows the SGS3 screen out of the water. Probably a closer fight with the more neutrally calibrated SGS4.
-Idle battery life so far is impressive. It's in the high 90's after using it first thing in the morning for a bit then letting it sit idle, where my SGS3 would be in the high 80's at this point.
-Very very responsive phone! I can't stress enough how much faster it is than an SGS3 and how little it lags! The phone, with its Qualcomm S800 is incredibly fast and responsive. After your first couple of boots (which seem to take forever), the thing boots up in seconds. The only app with visible lag is the camera app, which is mainly when you launch it (and even moreso when you launch it from the lock screen). Again, this is picking nits, and the lag is like 2-3 seconds max, and only stands out because everything else is so speedy.
-I haven't gamed extensively on this thing yet, but in general it seems to get much less warm then many Qualcomm S600 series phones.
-Qi charging works great. I've got an LG WCP-300 by my bed, and it works flawlessly with the phone, and charges pretty fast too.
-Side bezels are nice and small.
Neutral:
-Ceramic buttons aren't better or worse for me, just different. They are definitely "sharper", but to imply you could ever cut yourself on them is madness. They aren't sharp! Just a different materials choice over plastic. They are easy to feel.
-Not enough apps take advantage of full screen mode - it's basically Google Play books, Youtube, home screen (sorta), and possibly a couple others. I'd love for Kindle/most games to use it. Hopefully developers take notice.
-Speaker on the phone (the one at the bottom) is meh. Sound quality is mediocre, max volume is mediocre.
-Headphone volume & quality is fine - virtually identical to my Samsung Galaxy S3, which was considered good in its day.
-I'd envisage a world where they could shave almost 1cm off the bottom and 0.5cm off the top of the phone's bezels to make the phone more compact. For my hands, the phone is ever so slightly too tall. Shrinking the top and bottom bezels more would make it perfect. Because of this, I like the Moto X's in-hand size better than the Nexus 5 (however I'm willing to put up with it for a bigger/better screen).
-The camera is pretty good, OIS is seamless and rocks (you basically don't take blurry shots anymore - with my SGS3, I'd have to take 3 pictures everytime to ensure I got one that wasn't blurry). However, you do need to use the HDR mode to avoid getting washed out daylight pictures. The sensor is capable of good shots, so I'm hoping for a Moto X-esque firmware patch that improves the default camera settings at some point in the future.
"Bad"
-Not necessarily bad, per se, but we've been spoiled by the nice chamfered edges on the iPhone 5/5S, and the rubberized edge of the Nexus 4. The squared off corners of the Nexus 5 again aren't "sharp", but just less comfortable to hold than rounded/rubberized/chamfered edges.
-Plastic doesn't feel bad in the hand at all, but doesn't feel premium like an iPhone 4/5 or Nexus 4. Conversely, though, the back won't break like on an iPhone 4 or Nexus 4, so I can see why they are going with plastic over glass.
-Very very minor backlight bleed in the 4 corners (mainly the bottom ones) that's only noticeable on an all-black background, like during bootup. It only struck me because I booted it in a dark room, an because I'm so used to AMOLED, which has no backlight bleed.