The title and marketing would make it seem like this is a movie about hardcore gabber, but that is only partially the case. Despite that, if you lived through the 90s and went to gabber raves in Rotterdam like me, I think there is still enough to like.
Let's start with my gripes. I did not find the "troubled brother" very convincing as a real Rotterdam gabber. The main protogonist seemed inexplicably way more upper middle class than his parents. His affliction with gabber also seemed a bit superficial. If your first experience of raving in the early 90s as a teen was a gabber rave in the Energiehal with proper chemical stimulation, let me tell you: it would be extremely unusual for this not to be the beginning of an intense obsession. The ending also is a bit abrupt and superficial: after a little foray into the evil and criminal world of hardcore gabber, our young protogonist can put this all behind him to proceed with a serious life as a classical pianist? His hardcore seemed to have died quite quickly then.
On the up side, I liked most of the supporting cast, including the "villains". Though the story wasn't incredibly original (in fact almost cliche), there was still enough depth for me not to be bored. Though not everything about the raves was "period correct", much of it was done well enough to give me some goosebumpish flashbacks. You do get a sense of the intense energy of the music, the crowd, and the drugs. As a Rotterdam native it was fun to recognize locations.
In summary, I was plenty entertained despite the flaws and false advertizing.