One thing that Netflix does that makes me wow for a bit, is the simple and subtle effect while scrubbing / fast forwarding (across all devices).
First off they pause the video leaving the last frame, then they display small thumbs while you're scrubbing.
While scrubbing in Plex the screen goes pitch black, and the minutes / seconds start running, giving you no sense of where you are.
This really simple feature that Netflix have makes the scrubbing thousand times smoother, even though the difference is minimal. Really, really smooth UI enhancement. Should be fairly easy to implement on Plex as well. Those minimal jpg thumbs doesn't require many kb's on the server.
However, I love plex for what it is, just want to give ideas making it even better!
It is called media indexing and Plex already has that feature, you just need to turn it on and let PMS generate the thumbnails. This is not a trivial task. It takes time to generate these thumbnails. I have seen it take 2 weeks (24/7) for some very large collections.
Setting => Server => Library => Show Advanced => Generate Media Index Files During Scan
Nothing from a graphical standpoint or anything. a "dir *.bif /s" in your libraries can help you determine how many have been created so it's not to difficult to figure it out.