I just received my Nexus 5, and thought I'd give some first impressions.

• The hardware is as plain as the reviews have said, but I have no problems with it. Frankly, I like the back of this phone more than any other phone I've used. Far more than the glass back of the Nexus 4 and it's miles better than the chintzy plastic backs of the Galaxy Nexus or even the solid-feeling plastic back of the HTC One.
• I don't really understand the ceramic buttons, but I guess they won't break... They're sharp as hell, though.
• The Verge was talking about a white grille on the earpiece, but mine is black. Maybe they changed it. Aside from the clear plastic of the flash (and the occasional blinking status LED), this entire phone is 100% solid black. I like it.
• The screen is enormous. When lined up next to my Nexus 4 with the top of the screens aligned, the Nexus 5 is at least 1/2" to 3/4" taller. The screen widths are actually about the same, oddly. The effect is that the phone doesn't FEEL much bigger in my hand, though it's thicker so that does add to it.
• The phone is FAST. Holy crap. I've already tried scrolling through a huge number of photos (in my Dropbox photo auto-backup), and the phone has zero stutter when panning past hundreds of photos. This phone is blazingly fast. It's absurd.
• Kitkat is a pretty nice visual improvement for Android. The transparent status and button bars are going to take some getting used to, but it's mostly in Google's stuff so far, so I'll ease into it
• Another thing I'll have to get used to is how they've added Google Now as basically what lives to the left of your main home screen. If you're looking at your primary launcher page, when you swipe to the right you no longer get another screen for icons and widgets, you get Google Now. This doesn't bother me too much because I tended to keep all my app icons on a single screen anyway, but I'm sure it'll throw a lot of people off.
• I can't possibly evaluate the much-maligned camera when I've had so little time with it. All I can say is that I've taken a photo with it and my Nexus 4, and maybe the reviewers are seeing a different software version, but all I know is that in low light the Nexus 5 kicks the Nexus 4's sorry behind. I've attached some photos to demonstrate. Both of these were taken with no changes to the camera settings from stock (I don't recall ever changing the Nexus 4's camera in the time I've been using it). The 5 is the light one, the 4 is the dark one. Neither photo is particularly stunning, but at least the Nexus 5 is able to take a photo that lets you see what's going on in it. Heck, the Nexus 4 not only did a terrible job with the light levels, but the photo is still noisy as hell. The Nexus 5, as I said, isn't much better, but at least you can tell that this is a photo of a chair!
• I'm getting a little bit of the magic that Moto X users experience with the voice commands. It makes me wish/hope that the Nexus 5 were capable of the always-listening function. At the moment it's ONLY on your launcher home screen. You can't even do it in your search results window. I'm not sure why they didn't at least let you do it if the phone was turned on, or turned on and unlocked. That would have been great. Maybe they'll still do it.
• 4.4 is white. The icons in the status bar are white, the background for folders is now white, even the line on the stock keyboard's "Swype" gesture is white. The whole thing is a lot lighter. I think it still needs a little work, though. It comes off a little too plain, but it's not offensive or anything. It's just a little...plain.

That's about all I can think of for now. I've really only had about 30 minutes to play with this thing. I'm really excited but I can't base my final opinion on it from the amount of time I've had to play with it. Still, I can already tell that I won't regret the purchase. I do think it's an improvement on the Nexus 4. I don't know if it's enough to make anyone with a Nexus 4 upgrade, but I don't think you'll be sorry if you did. I'm not. If you Have anything older than a Nexus 4, then there's no question that this is an improvement.

Let me know if you have any questions.