Even though it hasn’t been that long, The Verge has reviewed both the Nexus 5 and Android 4.4 KitKat. Unfortunately it seems that the camera and battery life do have issues, but as far as the camera is concerned, there’s a silver lining: it’s a software problem not hardware and so it’s theoretically “fixable” in the future. The battery life seems to be inconsistent and I’ll only know when I use it or when AnandTech does their review; they run very rigorous tests, unlike most other sites. Apart from these two issues, I think I’m really going to enjoy using this device!
Update: I’ve quoted the conclusion of the KitKat review because it addresses something important in terms of Google’s strategy with Android now:
If you were to say that Android 4.4 KitKat was the biggest change to Android in two years, you’d be right — but maybe not in the way that you think. KitKat on the Nexus 5 is not KitKat as you’ll see it on other devices. The Launcher and other parts of this OS are exclusive to the Nexus 5. The big change is one that’s been a long time coming: there’s Google’s Android and there’s everybody else’s. Google’s Android finds its apotheosis in the Nexus 5.
Right now, you can’t separate out Google from KitKat and vice versa. How it will play out on other devices is still an open question. But if you don’t particularly care about that question, if you’re fully invested in Google’s ecosystem and services, KitKat is simply a stunningly good operating system that feels every bit as up-to-date and modern as iOS 7, if not more so.