I'm back from my holiday..
@ Sang:
1) I haven't finished this map really. I've just started. All I'm doing at the moment is creating some rooms for me to work in. Trust me, when I release the proper map things will look much better.
2) I save shading till the end. And there is Scuba Gear at the entrance to the underwater section. Wouldn't want Duke to suffocate would we.
Thanks for the comments I'll bear them in mind when I'm mapping.
@ The Commander:
I didn't know that, cheers.