Can someone please describe the academic quality at ISERC in Visva-Bharati? Is it comparable to the standards set by some IISERs and NISER?

Both are the decent Institutes. Visva-Bharati was declared to be a Central University and "An Institution of National Importance" .
Here, You are taught all the basic subjects such as Mathematics, physics, chemistry, biology, computer science, etc. For first 2 years and then on the basis of your academic performance you are allowed to take major in a specific subject in your 3rd year.
The quality and standard of studies is also good and focused for research purpose. But study isn't that deep.

You can check the other detail with the given below link.
http://www.visvabharati.ac.in/Courses.html

The academic programmes at NISER are deemed to be conducted through the Institute of Physics, Bhubaneswar, which is affiliated to Homi Bhabha National Institute. NISER insists on student evaluation of each course. Here, Students are encouraged to think in terms of making a qualitative difference in their learning outcomes rather than merely attend classes. You can check the other detail about it with the given below link.
http://www.niser.ac.in/content/education-niser

Hope it's helpful :)
Thank you !