Using it since last week. Software Centre is the most noticeable improvement I'd say. But updates are delivered right through it, not the 14.04 way, which was much better if you ask me. Apart from that, I haven't noticed much change.
But it has given one serious problem- it stays at black screen at full CPU load whenever I suspend the computer; then I have to force shut down it. My mate had it in 14.04 and 16.04 as well. But I have this problem only in the later version. It apparently machine specific problem.