The major change you may notice is that you can now see a visual representation of the web site. I.e. how it looks in mobile versus desktop. You still get the useful tips on how to improve your page speed for both mobile and desktop. I do wish they would also validate that you are properly doing the right SEO set up for your mobile or responsive design site. I know it is not a speed thing but I assume it is easy for them to validate.
Here is an animated picture:
As you know, speed and mobile are factors in Google's algorithms now, so testing is important in this area.
Forum discussion at Google+.