Not an easy question to answer I'm afraid. Some people get high from it, others don't. It all depends upon what you personally perceive as a 'high'. It's also very dose dependent, and finding the correct dose for you is also dependent upon the size of your current habit, so it involves quite a bit of trial and error.
It's also not as euphoric as heroin for example, but the right dose can provide a very long lasting, functional high.
However, if you take too much, it can be quite dysphoric. When I was on methadone maintenance, the general rule of thumb was 10mg equated to a 100mg bag of brown street heroin - though I think they were erring on the side of caution there - I personally would say 15 - 20mg per bag myself, but again there are many variables involved such as the quality of gear you're used to and your metabolic rate.
But to get to the point, if you're due to run out of your usual opiate but can get methadone it won't be a waste. It stops withdrawal in its tracks and lasts all day. However, it does take a while to kick in, so the trick is to not take too much in one go - otherwise it can knock you on your ass. How much is too much depends upon what and how much you're currently using. If you can provide that info, I'm sure someone could advise a reasonable starting dose. I'm only familiar with UK brown heroin, so my advise may not be relevant.