My son and I did Music Together for over 3 years and I love the music collections. My son still listens to them. We had started in Tucson, AZ for several collections and I was really pleased -- I also met some great moms and kids in the class. When we moved to Texas, I tried one class in Frisco and was incredibly disappointed with the venue and the teacher. She didn't want the kids to move around which is so unlike the whole Music Together philosophy! So I paused until I found a fabulous teacher in Plano and we stayed with her for much of our remaining Music Together experience. I have to agree with the previous poster that I think it depends a lot on who the teacher is --- my first experience in Texas as well as a few of the summer classes I took were not nearly as positive.
I suggest trying a class or two out with different teachers and seeing who you and your child fit best with. As far as the educational approach of Music Together, I was amazed at how much my son picked up over time -- a sense of rhythm, knowledge about different instruments and their sounds, and the ability to make up his own words that fit the Music Together tunes. Neat.