I have been taking L-Glutamine for about 2 years. It is the most abundant free amino acid in muscle tissue. When I first tried it, I noticed an increase is strength, but mainly a much faster recovery time. I am skeptical, so I had two containers, one with the Glutamine and one with powdered sugar. They were identical, except marked on the bottom. I kept a record and after being on both for 3-6 weeks, I did get a definite better result with the Glutamine.
I have done the same with creatine. With the biologic variation that is to be expected, I seemed to gain water weight with creatine. My strength would go up for about 3 weeks, then drop. I don't know why. I tried reloading, but it did not change.
So, if it works for you, keep updating your evaluation of the supplement.