Build quality, Lot of space for upgrades, lot of cooling options including liquid, etc, etc.....one can be happy with the basic Rs 500 cabinet whereas one cannot be with the most high end 15K one.. it all boils down to individual preferences..
Not for me to pre-suppose if the decision is already made and all that. But the NZXT Gamma has excellent build quality (not just for its price), has lots of cooling options (5 fans and including liquid cooling provisions) etc.
I am not one of those who suggests being happy with a Rs. 500 cabinet. Just looking for that particular place where utility and value meet. To avoid both under-utilization as well as over-spending. That is what I tend to look in most of my purchases, as a rule.
If you are curious, do take a look at the NZXT Gamma's reviews. I am sure you would have picked your case with lots of considerations in mind. All the best.