For a long while, the strongest opiate I would try was Oxycodone.
I tried Codeine, Oxycodone, Hydrocodone, Propoxyphene, etc.
I always thought that heroin and morphine would feel JUST like other opiates, only MUCH stronger.
I was way off base.
When I finally got my hands on liquid morphine, the door was opened to a whole new world.
Yes they are similiar in the sense I felt no pain, I was calm, and there was a lot of euphoria.
But the 'rush', the overall euphoria was so different, like nothing I could explain. It was SO euphoric it gave me a new mental outlook...in fact, Morphine, to me, is a lot like shrooms. My mental aspect on heroin/morphine is so different...I think clearly, I feel in control, it's absolute euphoria.
I can also attest to the visual aspect. Higher doses of strong opiates also give me visuals, sometimes very intense visuals.
Roxanol Intensol comes to mind in this area. I can lay in a dark room after plunging the rig for hours...just lay on the couch and see a whirlwind of rainbows flow across my mind...with a never ending smile on my face and nothing but pure bliss in my mind.