The first thing I noticed was how fast it started, even from a mechanical drive. So fast in fact that I missed the splash screen the first time. Awesome btw:

The new interface is very nice as well. I always prefer the darker grey interfaces anyways, and they have streamlined things and made them less chaotic.

The performance options are still pretty much identical, but Photoshop now uses the Mercury engine, which takes much more advantage of the power in GPU's. I'm not sure how effective it is on all filters, but just to test it, the Liquify tool on a very large image with big brushes.
The crop too l has had a major revamp. First of all, it keeps the cropped area centered. (very nice in practice) It can also be non destructive now, and you can rotate the image for angular crops, along with zooming in and out, and panning the image around now. The old crop tool worked well, but I'd have a hard time going back to it after this.

There's also layer filtering now, which is amazing for anyone who works with a ton of layers. You can sort them by fill, adjustment, text, etc. as well as their names, effects, modes, and even color.

There are a ton of other features too, but I haven't had a chance to really go through it yet. I suggest reading a full review, and downloading the free beta demo here.