WordCamp US videos are already getting posted online! I have already watched two of those I missed in person that are outstanding:
Aaron Jorbin and Zack Tollman talked about the technologies of tomorrow, and I guarantee you will learn new things. This talk, despite being about “tomorrow's technology” is actually super relevant to the rapid advancement of web technologies in 2015, and is a must watch for anyone interested in the exciting stuff happening with the web today.
And Rachel Baker did an excellent talk where she goes basically line by line on creating a WordPress theme that utilizes the WP REST API. It's the best walkthrough I've seen to date and helps make sense of some of the boilerplates out there.
Watch those two, and many others. There were so many great talks, I'm looking forward to catching up with the ones I missed.