I find that stuff like methadone is really quite strong, and I don't see how it isn't addictive. I figure it's to keep addicts alive while they get treatment instead of them getting a hot shot somewhere and ending up in a grave.
The brain quickly adjusts and the rush from the modafinil goes away, it was gone by my second dose - it feels rather more like a coffee but longer lasting and smoother / cleaner I guess, it's hard to describe.
I think most people seeking such drugs are actually self medicating and would generally choose normal if it was an option. While I do have access to stronger drugs I have no desire for them. I also take Amitriptyline which helps balance out the Modafinil and the two together with Modafinil in the morning and Amitriptyline at night have been really effective at treating my dysautonomia and keeping me on a productive even keel.
I am not an expert, but yes Methadone is addictive. It is drug replacement therapy, and Methadone is still a drug. The primary criticism of its use in addiction treatment is that it replaces dependence on one drug, like Heroin, with dependence on Methadone. A benefit of its use is indeed that it's a well regulated drug whose composition is known.
My understanding of why it helps in addiction treatment is that it triggers the same receptors as the drug it replaces, therefore satisfying the addiction, but it produces less intense effects and stays active for much longer, with less severe withdrawal symptoms spread out over a longer time period.