I'm around bag 30, and I really liked the inclusion of black highlights on the pillars in the interior scenes. IIRC the outer walls of MT are actually supposed to be black according to Tolkien, but I can understand not doing that since the movie depiction is what people have in mind. Feels like using it as a strong accent color for the interior is a nod to it.
Other than that, I am always impressed at how Lego models fill space efficiently. Whenever I try to build something big I use a metric ton of bricks to build height. The first set of inner walls shows a neat way of getting height with stability with the pin/axel connections. I also really liked some of the creativity in the assembly of the main gate details!
PS, sorry for being the one to bring up the Mumakil, but I saw the rumor and just got excited 😆