I am a huge fan of the D4. Have boxes from 1990 till present. Always has been a very consistent cigar but more on the medium side. For me it has been a great aging cigar and with 10 plus years on them they can be something special.
To many factors to go into on why you may not be getting any taste, such as storage, vendor, code, bad year, bad box, etc.
This is just my opinion, but I have not been happy with production as a whole from 2015 till present. When buying regular production boxes from 2015 on I try and find boxes rolled at a mother factory. The AMO 2015 D4's have been decent. But I have been more inclined to just pick up boxes with a few years of age from 2013/2014. The buying by code system is not flawless and does not guarantee you a perfect box, but I have had success with it. The PSP and HQ boxes the Prez puts out are always good buys also. Look around and see what people are buying and see what codes seem to be smoking well and buy off of that.
Also if the boxes where in the air long during shipping sometimes I have found it can take up to 3 months to acclimate to your humidor. Have smoked boxes off the truck and not been impressed then a few months later when I put one out it is a totally different smoke.