The growing relationship between a tall dwarf & a Sylvan Elf was new to me. I wasn't expecting there to be a love triangle in "The Hobbit," especially not expecting an Elf - Dwarf love triangle. A surprise for me that the Wood Elves would have a female capt. of the guards in "The Hobbit" movie. Added interest to see an interest develop between new character not in the book, and crossing racial barrier. Legolas has a long, long life and time to develop another love interest if the first one doesn't work.
Long legendary epics with wars, having interesting love stories, strife, woven thru it adds to the substance of the story.