I've had this question for a longer time - but from another point of view ... personally, I don't like opioids. Really. They don't work, or my genetics don't work with them. At best (like for butyl-fentanyl or AH-7921 - the atypicals.. and I have done AH from anything between 20 and over 200 mg) it's sort of a better benzodiazepine, calming to sedating and to get rid of bad thoughts. But euphoria?
Then there are the structurally typical ones, like heroine or oxymorphone, also methadone. They tend to have a weird synthetical stimulation to them - even with a low dose of good quality heroine I could not sleep half of the night, despite taking clonidine which otherwise always puts me asleep.
Also I have some ugly kind of "natural" dysphoria or anhedonia. Well, that is why I tried so many drugs, at least part of..
But it's not that I can't experience good feelings. It just does not work as expected.. I think dopamine is what really makes life glowing, at least for me. On some occasions, a DRI combined with a low dose of NMDA antagonist brought me into sunny euphoric bliss that felt just so pure and natural that I had tears in my eyes of unexpected happiness. And -that- feeling I really crave, yes- Opiates are nothing in comparison (thankfully, maybe).
The next thing that might come close, but with a huge difference in that it feels ..different, seems to be a flood of serotonin. This has that "just watching the world is enjoyment" kind of effect- but tolerance sets in soon and there are many drawbacks.
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Well- I'm really wondering if my endorphine system does not work.. maybe genetically?