Science is defined as a systematic study of the natural and physical world around us through observation and experimentation. If we apply this definition to the process of Krishna consciousness, we will find a match.
Bhagavad Gita is an exposition on Krishna consciousness. It gives a detailed psychological presentation of what it means to live and work in this world of pain and pleasure. Then, it gives a systematic guideline to the metaphysical side of things and then it integrates both the worlds. There is no doubt in mind that Krishna consciousness is a systematic psycho-metaphycial analysis of reality as a whole.
The difference in observation and experimentation between modern science and Krishna science is location. Modern science observes and experiments things and people on the outside. Krishna science does the same on the inside. In other words, when we demystify our own internal self with the help of literature, advice from a teacher and daily training, we can prove or disprove the process of Krishna science.
In my opinion, it is no less scientific than mainstream science!