My overall favorite room in season 3 is the Quicksand Bog. While it's still one of those bash-the-wall-or-hit-an-actuator rooms, at least it's filled with pseudo-quicksand. Plus, climbing a slide? Much harder than standing in an elevator twiddling your thumbs. That's a hardcore room.
But the most improved award definitely goes to the Chamber of the Sacred Markers. The center rooms always looked thrown together in the second season (Medusa's Lair had the same Heart Room paint job, but with the head of Medusa at the front - oooooh, MEDUSA'S LAIR), and they put some serious time into the Chamber. Plus, as others have mentioned, there's the sweet center shaft where temple guards can hide and terrify innocent youth after opening the door. Actually, now that I think about it, this is also a hardcore room.
The Room of the Ancient Warriors kind of made me upset. The door between that room and the Jester's Court had to be pulled because of space constraints (I would think), and that reduced the possible temple layouts and choices the contestants could make. The idea was good, but in practice, I don't think it worked as well as it should have. I like temple guards grabbing people in the suits of armor, though. Wow, now that I really think about it, all the new rooms were much more hardcore than the ones they replaced.