Since you have opiate experience, you'll be disappointed. It's not much of a high, if you do feel anything, it'll in the first few days, they take you up slow enough to the point where you don't really feel the increase. Not feeling high is also partially attributed to the substance that methadone happens to be.
This is not a universal fact, but methadone clinic, for a lot of people turns into the place to go dose, score some benzos and nod for the rest of the day. You get into "methadone slump," at least that's what they call it around here. I'm not saying that this is going to be you. I'm just sharing my experience.
Like I said in my previous post, I'm not trying to discourage you from the MMT, I'd rather someone doses at the clinic than doing shady shit trying to score dope.