I love the way my Nexus 5 runs. I use it just as much as my iPhone 5 and although it doesn't have the same UX niceties, it's still plenty smooth and fast.

What really frustrates me is the camera. Some photos are great, others look like the image has been made deliberately bad. I don't think the Nexus phones will deliver a great camera experience any time soon, and there's only so much compensation that G+ can make to a dull, blurry photo.