What is opnion about ISI Kolkata?

The best course area ISI Kolkata has mastered until today is PCM. It is one of the premier institutes of India and is offering masters in several fields concerning research on Statistics. 

Apart from that, this institute offers 2 UG programs, namely B.Stat and B.Math. The entrance exams to both of these courses are considered to be highly difficult to ace. The entrance exams are relatively even more difficult than JEE-Advanced. 

A major difference between ISI Kolkata and other institutes is that they only enroll around 30-40 students per year, to help keep its value intact. 

Quite clearly, it is a very demanding course area. If only you are typically inclined towards the subject area, you can take it up as a future career, since it is extremely fruitful if aced.