The death of Kurama was apparently a shocking turn of events in Boruto. However, this twist does nothing but prove that Naruto's sequel is still struggling to get away from the flaws that plagued it since the beginning.
Kurama is the nine-tailed fox demon that was bound to Naruto at his birth, to stop it from rampaging and destroying the village of Konoha. This event not only killed Naruto's parents but set him apart from the other villagers, many of whom had lost loved ones in Kurama's attack and saw Naruto as a monster. In time, Naruto was able to overcome these prejudices and even developed a positive relationship with the spirit inside him, turning Kurama into a friend and, in the process, into a fan-favorite character. In chapter #55 of Boruto, Kurama sacrificed his life to save Naruto from the lethal aftereffects of a technique he used to protect his son Boruto and his protegè Kawaki.
What was supposed to be a shocking twist, however, exposed Boruto's flaws even more. First of all, it proves that the series still needs the characters from its predecessor, mostly Naruto and Sasuke, to get fans' attention. Killing Kurama means a major change, but for Naruto, who is supposed to be just a secondary character now. It is true that in the last fight Boruto and Kawaki had to handle things and Naruto and Sasuke have been sidelined, but they're still there, constantly "on screen", making meaningful decisions that impact everyone else. The death of Kurama has no direct effect on Boruto or his fellow young ninjas, so it looks like the authors just wanted to throw away a beloved character for the sake of having something relevant happen, and it did, but it just did not happen to the right character.
Boruto makes a big effort to look as different from Naruto as possible, but without ditching Naruto's setting, which ultimately proves to be a contradiction. The villains of the sequels are cyborgs or the godlike aliens of the Otsutsuki clan, rather than just rival shinobi. Boruto also focuses more on technology as a source of powers, making ninja techniques less relevant. However, this proves to not be enough, as the main setting is still the village of Konoha, and all the ninjas of the older generation are still around, inevitably grabbing fans' attention. The death of Kurama proved that this issue is real, as such a major plot twist was applied to a character who should not be the protagonist anymore. There are only two possible results: either the death of a beloved Naruto character is dismissed as something secondary, or it brings even more attention away from the supposed protagonists of the manga.
The only way that Boruto could have avoided the cumbersome shadow of its predecessor was to set the story far away from Konoha, and to show Naruto as rarely as possible. However, the manga did not have the courage to do that, so now it has to struggle with secondary characters who take the attention away from the protagonists. Killing Kurama was probably a further attempt to "make things different" from Naruto, but as a major plot twist applied to a secondary character it ended up having the opposite effect. The death of Kurama just proved that Boruto will never overcome its biggest flaw.