I think only the Nexus 5 started to catch up with the 4/5S in terms of speed and build quality. And it's only with CM11 on the N5 that it begins to reach the "smoothness" of Apple's UI (and yes, I know there are some tricks used).
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.