Cool. I wondered about this one as well. I liked the level - those two chambers reminiscent of M2's Thoth AI rooms were nice, and easily recognisable. The octagonal room area certainly gave the feeling of containing plenty of secrets.
The duct system was interesting - it took me a bit to notice I could grenade up where necessary ... a surprise as has been said, but nothing we can't handle :). The fact that you had to come back to the ducts a second time was a pain, with the far off opening switch and race back, and the 'circuit' system was interesting. The switch that opened that section of wall could still be pressed after hitting the circuit, which I think messed me up the first time and I was quite confused about getting to that last lift in the ducts - yet another re-entry.
