Oh! This is right up my ally! The sun has an apparent magnitude of -27 while the full moon has an apparent magnitude of -13. So the sun is ~400 times brighter than the full moon. The average distance between stars in the globular cluster or "core" (which by its nature has a vague boundary) is only 1 lightyear, which is important in that it is less than 10 parsecs ~30 light years. Stars in the core tend to be older giants (and therefore brighter) with typical absolute magnitudes of ~-3-4. The absolute magnitude of a star is the apparent magnitude at 10 parsecs. So the stars would appear to be much brighter to someone standing on the planet. These could even begin to rival a full moon and of course you have dozen upon dozens of these things near by so I would say the artist rendering doesn't have enough bright stars and that the star are also not bright enough. Additionally the super-massive black hole at the center could be even brighter some reaching absolute magnitudes of -28! but that is of course only very close to the exact center. The real problem is that all those stars would screw with a planets orbit so its unlikely any planet could actually support life in the "core". Now back near the edge then sure a planet might be able to survive and their night sky would problem look something like in the picture.