One of my friends is an alumnus of ISI Kolkata and here is his insight into the placements for MTech CS. 

1. The job profiles offered by ISI are mostly from Data Analytics. You will not get many CS core jobs from the placement drive. Don’t expect companies such as Google, Amazon, Microsoft, etc. 
2. As an M.Tech(CS) student, you will have a fair knowledge about IR, Pattern Recognition, Data Mining and you can easily get jobs at these visiting companies. 
3. In the recent placement drive, the highest package offered was INR 25 to 28 LPA while the average was INR 10 to 12 LPA.
4. ISI offers good job opportunities, but it is limited to a particular domain. Along with Data Analytics companies, few R&D centers like TCS Innovation, Infosys R&D, visit the placement drive. 

Other than that you can apply for summer internships and if you perform well you will receive PPOs. But if you are expecting a job strictly related to your field after the compilation of your masters then don’t choose ISI. It is an excellent option if you want to do a Ph.D. or want a career in research.