> How is failure or success determined? Did we know what the goals were for decriminalization?
I think supporters would say that ending an approach that has failed miserably across multiple generations is a success unto itself. And that the bigger goal was to open a path to a wider rollback of the drug war.
> Was improving drug purity a goal?
Saving lives is always an explicit and implicit goal in public policies around health. Drug purity saves lives. Especially these days.
> Were legal markets supposed to appear? Was it supposed to reduce access to minors?
No. It is basically a government mandate for people to hand their money directly to the criminal drug dealers.
> Was some mechanism for connecting addicts to social services to help them supposed to appear?
To be fair, Oregon has taken other actions to fund services for addicts, like diverting funds from their marijuana tax revenue.
Most people probably want a drug policy that leads to a) fewer dead people and b) fewer addicts and c) reduced crime. Personally, I also think we need to consider liberty as one of the top goals if we're going to judge a drug policy as successful or not. But even in that respect, this law did very little.