I'm part of the over-burdened LOTR fandom, although I dip a toe into many, many fandoms. I know a little bit about a lot of fandoms. But, I love my Tolkienites best. I enjoy 10th Walker stories, canon pairing stories except for Aragorn/Arwen (Arwen's such a dry character that I just can't get into her), and Girl-In-Middle-Earth stories.
What I don't like are the unbelievable stories. Make me believe that your characters are in love. Give them depth and character and soul. Make them more than words on paper. I want to know who they are and who they're not and why they are the way they are--but I want to know that without being told that. I want to be shown that.
See, I love Legolas, just like you. Or I love Faramir, or Eomer, or Boromir, or Aragorn, or Haldir, or Erkenbrand, or ... But what I don't love is being told that someone loves someone else. There has to be a reason. I'm attracted to a lot of people, but I don't love a lot of people. I can appreciate an attractive man without falling in love with him. I can even get turned on around him--all those "hand touchings" that are so important in LOTR fanfiction--but still not love him. Wanting to have sex with someone is different from loving them.
And another thing about Legolas--if you pair him with a human, realize that your story has to be LONG and ANGSTY. Because there are four successful elf/human pairings and one unsuccessful elf/human pairing in the history of Middle Earth, and it's completely, absolutely legit for your story to be the fifth successful pairing. But what's not legit is for it to be easy for them.
Also, what sets elves apart from people isn't that they're faster or better or whatever. It's really LACE (the Law and Customs of the Eldar). And we all hate LACE, but the truth is that if you ignore LACE, you've basically just made elves human superheroes. So either make up your mind to be completely AU from the get-go and WARN YOUR READERS that you're not going to follow LACE (so that I know I'm not going to like it) or
I encourage every author who would write a Legomance to REALLY consider writing...:an Aragorn/Arwen breakup story (in movie-verse, just have her get on the damned boat), resulting in a non-canon Aragorn pairing a Boromir lives story (your 10th walker gives him his shield, tackles him when he goes off after frodo, takes the arrow for him, cuts the bow string, tells everyone that she has had a vision of Orcs coming, she heals him in Minas Tirith, she heals him in Amon Hen, whatever), a non-canon Eomer pairing (this is easy stuff, Lothiriel is a note in an appendix, no one cares about her) a Gimli-mance. Why can't he get some? Heck, make it a tragedy and she croaked off prior to the ring war. a Thorin/Fili/Kili-lives romance. I've seen several of these done really, really well.
And so on. These are the big headings, but there are HUNDREDS of Satisfactory-to-Good Legomances (most of which aren't completed, but, most fanfictions aren't completed), and these other characters get snubbed.
Why do the other characters get snubbed?
Because elves are perfect. It's a lot more dangerous to love a human than an elf, and it's a lot harder to write about the angst that goes with that. Once your elf binds--that's it. No cheating, no old age, no death, no problems forever. Whereas humans are imperfect. They cheat. They grow old. They grow bored with their lovers. They're harder to love.
Anyway, I hope you write well!