Depending on your body chemistry and if you have the right liver enzymes, tramadol can be a pretty decent opioid.
Tramadol itself is a parent drug and has very weak mu agonism. But when taken orally and converted by the liver, around 1.5hrs, it becomes O-desmethyltramadol and is a very decent opioid in my opinion. It also weakly releases serotonin (i.e. - meth, mdma) but is also a reuptake inhibitor of serotonin and norepinephrine. This is why you hear people referring to it as "stimulating".
Tramadol also has effects I believe on nicotine receptors, ndma receptors and some other obscure receptors that nobody talks about, which are unique to tramadol and not typical of other opiates or opioids. Some may find this dirties up the experience, but I actually enjoyed some of the unique characteristics.
O-desmethyltramadol is a full agonist at the mu-receptor. And kratom is only a partial agonist. So I don't agree with the person who said kratom was stronger than tramadol. Although it could be for people who lack the liver enzymes needed to convert it.
I was addicted to it for over 10 years. 400mg spread out through the day was my usual dose. Some times it had me nodding as hard as heroin (which I didn't get to try until later on in my opioid career). It made music sound incredible and gave me boundless energy as well.
Anything under 400mg either didn't work at all or had barely perceivable effects. I'm not sure why this was. Even when I would go through withdrawal and come back to it, I still had to go up to 400mg to get an effect.
So if you have a low tolerance and the right enzymes, tramadol can be pretty good.
I found now though after having done heroin and buprenorphine for years, that the magic to tramadol has some how disappeared (even with tolerance breaks). Maybe my liver changed as I got older or something, but it just doesn't hit me the same way it did when I was in my 20's. But I still have very very fond memories of things I use to do on tramadol. I absolutely loved it.
I also went through tramadol withdrawal every single month from the ages of 19 to 30. It is a horrible experience that goes beyond just the physical opioid symptoms. I felt like I was completely losing my mind on tramadol withdrawal. And to think most of those years, it was marketed as "non addictive". I don't regret my days on tramadol though. I think it's a complex synthetic opioid though and there are so many factors that can influence whether or not some one will have an enjoyable time with it, nothing or even a seizure.
Everyone is different though, so it's amazing how many differences there are among people trying the same drug.