Prequel ✔
Uninteresting character ✔
Gonna be a hit for sure.
Wut
Gollum's the most interesting character Tolkien created and the one with the most depth and complexity.
Makes you wonder what he witnessed, or experienced himself, for him to have that much psychological insight to create such a nuanced cretin that is both sympathetic and loathsome.
Gollum is a cautionary tale about dangers of immorality. The loathsome part is easier to explain then. He's Frodo's evil twin, someone who could not resist even the slightest temptation, because he had no desire to do so in the first place. It's pettiness, and that's where you get both sympathy and loathsomeness. Throughout the book Tolkien states, in accordance with his Christian convictions, that it could happen to anyone. And that's the reason Gollum inspires disgust rather than hate. He is not a threatening enemy, who would cause fight or flight reaction, he's more like a leper you don't want to touch because you instinctively feel that it might be contagious and you might become one too. You can vaguely relate to Gollum, because his concerns and desires are so mundane. He is evil out of weakness not strength. And here I also recall Nietzsche's concept of pity as disgust. You can only pity someone you feel is beneath you. So the two are actually linked.
In Tolkien's case, it's also easier to feel sympathy for Gollum because it in fact did happen to everyone. No one was immune, including Frodo. Also, it's interesting that Sam seemed to be the most resistant to the power of the Ring, seemingly because he is a simple man. I believe he wanted to use the Ring for gardening. You can either interpret this as paternalistic admiration of the one underclass man who knew his place, or admission that power corrupts, even if it's just intellectual power like in Frodo's case. There's probably a bit of both in it, although I lean for the latter because even Sam's designs for gardening were grandiose.
Also, in terms of relatability, it's interesting to compare him to Sauron, who is completely depersonalized. And the same goes for other characters too. The more powerful they are, the more distant they are. On the other hand, when Saruman loses his power, he becomes little more than a thug. So the only thing that changed was his ability to do evil, not his personality. Which goes to show that in some fundamental ways, even someone like Sauron is like the rest of us, and the same goes for Aragorn for that matter. So Tolkien also ends up making an argument against blind hero worship, even though his critics often argue completely otherwise.
Finally, I'm also pretty sure that Tolkien witnessed terrible things and thoroughly immoral men in the trenches. And moreover, they were probably decent men until war made them evil.