W00t, loads better then my first map.
Anyway, it's not going to be playable in any fashionable way, obviously, but it's still a very good map for starting out I can see

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The archway you got there leading in to the displacement tunnel should really be more detailed. I say use either displacements or the arch tool to generate some funkier roundingoff. Or you can do it by hand with brushes if you feel like it.
If you use the arch tool or do it by hand, though, don't forget to tie it to a func_detail when you're done.