It's a marvelous mode... It actually used less artificial processing of the image. I've done a lot of comparing HDR shots between it and other phones like my wife's S7 and I can see some clear differences.
The S7 (and phones like the LG G4) seems to merge the source exposures together then process the image like it would a normal shot. End result is an image that had improved range, but the processing artifacts are not any different than the non-HDR version.
HDR+ doesn't so much fix exposure as it does reduce noise. But since it does that via a pixel by pixel comparison between exposures, rather than comparing a pixel to the ones around it, the end result is an image that preserves much more of the actual subject. Any noise that is left is a more natural, pleasant looking grain. It's as if the process effectively increases the size of the 6P's sensor.
Which is no accident since HDR+ basically borrows it's approach from the tricks astronomers use to improve exposures from telescopes... Where any information added via artificial processing is useless information. They only want what the telescope saw, not what an algorithm spit out.