If we look at the war on drugs as strictly a matter of policy, of course it's a failure. Rates of addiction have been fairly steady and drugs are more cheap & plentiful than ever.
But I think it's more interesting to look at the war on drugs as a success...as a means of social control, as a means for a certain segment of the population to gain wealth & power, as a political wedge issue that enables politicians to stay in office, etc.
I'm for the legalization of all drugs. Would there be problems because of drugs being legalized? Yeah, probably serious ones actually...but I'd rather live in a society that has to contend with those problems than one which has to contend with the other set of problems that arises from prohibition or even decriminalization *shrug