I've touched on this idea before, but not once has anyone taken me up on it. Basically it's this -- I challenge you to find a single well-written Tolkienesque fantasy novel that did not sell well. Honestly, I would love to know if there is one. I am fairly well read within the fantasy genre, and I cannot find even one. In other words, my idea is that if writing a good Tolkienesque fantasy always sells very well, then it is as close to a sure thing as one can get in publishing. So then why would agents pass up a well-written Tolkienesque fantasy novel?
I don't count the official Dungeons & Dragons books, because in my opinion they don't fall into the category of 'well written' (with apologies to the many people who really love Drizzt). I count books such as The Sword of Shannara, which was a blatant rip-off of Tolkien that was a mega-best seller, and McKiernan's Iron Tower trilogy and Silver Call duology, which were also extremely blatant in their following of Tolkien, yet again they sold very well.
My books do not copy any of Tolkien's plot lines; they merely dwell within the Dungeons & Dragons/Tolkien-style world that I grew to love so much as a young D&D player. I purposely set out to avoid what bugs most people about the official D&D books, i.e. that they seem to much like a game, are not realistic enough, and have plasticky characters. I wanted mine to read like a true, well-written novel, but set within a D&D type world. There are a ton of readers out there who never want to see another elf or dwarf in a book again, and more power to them, but they would be wrong to think that there aren't also a ton of readers out there who crave more.
So, I challenge any agent to show me a well-written Tolkienesque fantasy book that didn't sell well. I would love for that agent to tell me why my books shouldn't be given a chance, since they fall directly into the category of 'a sure thing' (not to mention that Game of Thrones and the Hobbit movies will draw a lot of attention back to epic fantasy).