Whilst they say it might look largely the same, the player has been completely rebuilt to be fully responsive and to suit as many of the vast array of devices out there now that it possibly can do.
A big feature of the player is the fact that it's apparently much faster now, with many videos apparently starting in less than 1 second.
I was also excited to read that they've paid real attention to accessibility issues so the player has full keyboard support and conforms to WCAG2AA. I'm yet to test the keyboard controls for myself but this is something I haven't always found with other players - even if they offer keyboard controls they're limited and don't actually help with starting a video. As part of this accessibility work videos on Vimeo can now include captions and full subtitles.
For those of you not familiar with Vimeo, it's kinda like YouTube in regards that it's for uploading and watching videos. But it has a feel that it's more for creative works than for skateboarding kittens.