The unparalleled status of the aNu-bhAshya in the world of Vedantic works is due to the fact that it serves as an index to the brahmasUtras, while at the same time qualifying as an outstanding stotra on the greatness of paramAtma and the shAstras.
The founder of every school of Vedantic philosophy has, naturally, interpreted the brahmasutras to show that it conveys the meaning as propounded by their own school of thought. Prior to the bhashya, or commentary, of Shri Madhwacharya, there were at least 21 main interpretations of the brahmasutras already in vogue. Needless to say, each of those commentaries had superimposed their own philosophy on to the sutras, leading to their distortion and misinterpretation.