I love the concept; it's interesting the way you dithered/faded out the top to go into the interface, and I admire your ambition to take on such a large piece, but I think it's suffering a bit.
The main thing is repetition: the arches, the columns, the bricks, the floor--all are very repetitive. This may be do the size you are trying to take on, which I guess you really can't do much about, but on a smaller resolution, I guess it'd be less noticeable.....and I see that you tried to break it up a bit with different colored bricks and the glowing cracks, but I still think it lacks. The simplest route you could take is to add things like ivy or cracks. Good luck in this department...
The other thing I noticed, small I guess compared to the former issue. I think that the latter could stand out more...it just blends in with the corridor.
But otherwise, a solid mock up. You could maybe do something interesting with the interface, but that's personal choice. Can't wait to see this finished.