I like this one a lot. It was a great dynamic image of the duel by (and in) the fountain. Ecthelion grappled the monster and pulled it into the fountain, which you have deliniated in fine style. Tolkien always imagined his Elves as being physically powerful beings, so this one might have earned his approval in that respect. The size of Gothmog is not something I am too worried about; there are some indications that the balrogs could modulate their size, or suffer a loss of it in certain circumstances. It's enough that Gothmog is larger than a man, or even a tall Elf, and demonstrably powerful in an infernal manner.
Thanks. This is a tricky one. You have make the balrogs formidable but they also have to be within a physical range for the elves. You can't have giant elves or Balrogs. I think that Tolkien was aiming for creatures of a more understandable proportion.
Tolkien seems to have changed his mind about their size a time or two as well. He emphasized the menacing power and strength more than overt physical features, so that has been my big criterion for determining liking a picture with a balrog in it.