For someone like me that could not attend WWDC 2015, Apple has released the video to watch online or download offline here. Also, if you want to download all the videos in one go, just use this script.
There are eight featured videos on the main page, The first video is of course the keynote, two of them are about the new Apple Watch which will be available to purchase soon.
Another one is about IoT e.g. how to create fake hardware to communicate with software while there is no real hardware to test your app e.g. integration with HomeKit.
Also, another one of them is about deep linking of search API in iOS 9. One disappointment for me or maybe other people as well, is that there is no new shiny hardware announcement this year. I thought there will be a new iPhone 6S or something similar.
So, I think this year they are really focusing on the Apple Watch because there are two featured videos about it. So, the new shiny hardware is the watch itself but they just did not announce it publicly. Well, I have a concern about it though. Until now, after I went to Apple office in Sydney to attend the lab (I am still have my weather app for the watch waiting to get approve), I never see anyone wearing the watch on the street or anyone I know is wearing one. I know that you have to order it online only for now and they will allow you to go to Apple store and buy it soon. I am not sure about the US, I heard that they have about a million online order. If you live in the US, please let me know if you see someone wearing the watch or if you know someone wearing it.