P: The Cmd key selection is totally messed up.

Using the brush, now I have to click the Move tool to select another layer. Before I was able to choose it by pressing the command over the other layer. (this is not happening with auto-select unchecked)

It sounds like you are both seeing the same issue. I can reproduce on my macbook pro and 10.9. Are you both on 5K machines? El Capitan?

App frame on/off?

It might help if we have a movie of the behavior you're trying to describe so we can try and repro.

I have installed the latest version of Photoshop (2015.1)

This includes the re-designed UI which will take a bit of getting use to but is cool.

However I cannot select multiple layers. Command+Click seems buggy. It works then it doesn't or it lets me select a couple of layers then drops them all when I command click on another.

Very frustrating. Is anyone else experiencing this.

I'm using an iMac (Retina 5K, 27-inch, Late 2014)
Processor: 4 GHz Intel Core i7
Memory: 32 GB 1600 MHz DDR3
Graphics: AMD Radeon R9 M295X 4096 MB

Can you be more specific about your issue? (provide clear steps to reproduce the issue)

What version of Mac OS are you on?

What are you command clicking?