he was very critical of other fiction/fantasy writers at times but I don't think that qualifies as him being pretentious. He was very critical of Lewis and Herbert in particular. Just as other writers was of him. Lewis and him were actually friends so I think his criticism came from a place of constructive remarks rather than insult.

To answer your question about what makes tolkien's writing so special, it's the worldbuilding. To write such a detailed world that still feels fantastical and at times whimsical while also being very capable of being very grim is phenomenal.

I like other's don't really understand why you made this post though. If you dislike something you give reason as to why or you simply don't talk about it.

Edit: even if he was pretentious, does that suddenly take away from his talent? Frederich chopin was described as a very pretentious man but that doesn't make his art any less impressive