This was always a hard place for me to imagine also. So vast and dark... Jackson came pretty close to my vision though, how about you?
On a more serious note, if Moria was a trade center for the dwarves why is the path to the west so narrow and hard to negotiate. I can understand a few tight spots like the bridge that Gandalf falls from, but it seems the whole place is difficult to get through. Also, I always pictured the gates on the west as being bigger, but maybe that was just me.