Things I like: highly orthogonal & minimalistic design (basically vectors and functions acting on vectors), easy C FFI, well documented, satisfying to minify production code, my inflated salary (+job security for some).
Things I dislike: proprietary, impossible to skim, APL/J/K "culture", over-marketed, functions/operators overloaded in very unintuitive ways, lack of lexical scoping, interpreted languages falling out of vogue.
Overall, I recommend every coder to try K (or J or APL) at least once. They compare favorably to NumPy/R in many respects.