The q language is very powerful, and expressive - interesting mix of lisp and APL. You can do really powerful analytics without writing tons of code for it.
You really have to see how fast KDB is compared to most nosql products out there.
I barely did any q / kdb; only made a functional and usable UI, and did some prototyping of new ideas in other languages (Java, Max/MSP, Csound). I spent some time looking into q and was thoroughly baffled. Still am. It was really, really fast, though!
As I vaguely understand and can explain it, the k/q system made it easy to do fuzzy searches and deal with missing pieces of data. If the user missed a note, or our pitch detection failed, or our source data was bad, we were still able to find matches. (Yes, I wish I'd been able to understand this more at the time. Bygones, now...)
Sure, you can do the same in R or python, but the whole process is very quick and easy in q.