Got my set the other day *happy dance*.
I agree with Giles' assessment that the cards provide some great and imaginative challenges and I love the idea of using a standard set of terrain to use as objectives and/or red herrings. Bravo Joe and Osprey!
I do wonder if they'd complicate some of the more challenging scenarios in the books, but I can imagine, say, the Worm Hunt scenario really taking off with the cards.
I think using them in multiplayer games could also make things tricky, unless each player has his/her own set of terrain.
But all-in-all a great expansion!