UI
Recently I've been working on replacing some of the placeholder UI styles with curved edges and button styles.
Here's an example of how it started off, last year. Everything was just a different shade of crap:
And here's how it was in the announcement video. A nice 3-way gradient was created to be used in all the theming, and the general design changed to 'fun, colourful, contrasted against transparent black'. These were still using the stock UE4 buttons:
Recently I had another UI element that was looking too sharp, so I added curved edges and was blown away by how much nicer it made everything to look at (which is easy to test when you're developing and iterating for hours at a time). I then extended the curved edges to every border and fell in love with it. I added this to the buttons to, and gave them an embedded-looking border to stop them seeming like they're just sitting on top of the UI: