The Hero 3+ is a good step up from previous models. I have tons to say about it, but I'll keep it short and just list my favorite improvements and features of this camera:
-The lens is slightly bigger than the regular Hero 3 black. This increased the sharpness of the image quality a fair bit.
-Audio recording has been improved
-It is much smaller and lighter than ever
-The battery length is 25% longer than the Hero 3 black
-It is only slightly delayed (maybe 1/4 of a second) on the live preview on the GoPro app compared to about 3-4 seconds on the hero 3 black.
These are my favorite features of the 3+ black. I have been using GoPros for several years and they just continue to get better. I am a cinematographer and use these all the time, so if you have any specific questions for me, don't hesitate to ask!