I like it pretty good, I also have it on my Nexus 7 and it seems to help with the battery life.

I personally don't have one, but a friend of mine has a Nexus 5 and while I've "played" around with it, I really enjoyed it.

Whether it's the beefy hardware, or the Android 4.4 optimizations, (or a combination of both), the UI is silky smooth. I've also compared Angry Birds Go on the Nexus 5 and my HTC One X side-by-side, and while both games run smooth, the Nexus is smoother.

As for KitKat, it's a bit weird to use Hangouts for everything, but you can always change to a different app. I still don't like the app drawer though. I don't know why Google isn't borrowing some TouchWiz or Sense 5 elements, like being able to create folders in the app drawer and all that stuff. The stock launcher is quite scarce when it comes down to the app drawer, and it's been like that for ages. Perhaps Google considers it low priority...

Do you have Android 4.4 on your phone?

If you do, how do you like it?

I have it on my Nexus 7 tablet and am happy with it so far.