I like the hit-dice healing mechanics. I find it represents well how a character can find its second (or third, of forth) wind.
I also like how it can translate into D&D the cinematic trope where the hero(es) is beaten down, defeated or forced to surrender, then something happens and the hero is suddenly rejuvenated.
What I'm a little annoyed with is how easy it is for characters to recover all of their resources, and the lack of a wounded condition that would complicate natural healing. The DMG offers a few solution, but it quickly goes too far in what I call the "attrition game".
Thankfully, 5e is super flexible and houserule-friendly. The Solution to remove the auto-heal on long rests is interesting (or half it). An abstract "wounded" condition wouldn't be that hard to implement either.