OK, after limited use, it feels a bit faster (definitely faster than the beta), but the biggest difference is in color rendering:
ACR 3:
ACR 4 based on a color checker chart that I shot:
ACR 4 Camera Neutral (out of the box):

This last one might be the best of the bunch. What is so striking about it is that it is getting the purple better, but leaving the blue line blue, without adding a ton of noise (really almost none) like I was getting when doing it by hand.
You need to download the new profiles
here, where you can also get there profile tweaker (the DNG profile editor, you can only build profiles off of DNGs, but you can apply them to anything). The chart option on the profile tweaker is really pretty cool.
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Hmm, after posting I see these are showing sRGB limitations, the difference is more striking in a wider color space.