More than the UI widgets, I think the key part of the interface of a video player is whether the program is smart enough to (at least offer to) resume playing a video from wherever it was when that file was last closed.
It has always slightly boggled my mind that VLC, and many other players, don't do this.
MPlayerX (for OS X) does this, but personally I would prefer if it didn't. But that's probably because I watch a lot of short clips I'd rather have restarted, than long movies which I'd want to keep watching where I left them.
It has always slightly boggled my mind that VLC, and many other players, don't do this.