The only applicable critique is that original Buddhist doctrine is too general and allows flexible interpretations, nevertheless lots of scholars would maintain that Buddha's approach is one of the earliest attempts of systematic study of the mind using an imperfect method of introspection (famous Upanishadic neti neti doctrine is, perhaps, the earliest known to us), leaving validation of the insights to everyone who wished to follow the same path.
Buddha's investigation into the nature of reality and mind, which obscures it, is qualified for philosophy - precursor of modern sciences, not a religion (there is literally nothing to be saved). Theology has been developed by various competing sects hundreds of years later.