I love the graphics on the new "Ocean Bvld" course in Watopia, the underwater tube is cool, and I love the huge trees in "Jurassic Park" and even the dust on the gravel section by the marina!
But I like the hills too - I find a totally flat course kind of boring, especially as short steep hills are a great reminder to stand (riding the stationary trainer for hours always makes me a bit numb), and provide a great place to attack when the drafting effect is lower for the wheel suckers.
What do you think of the new expansion? Looks like there's a "mountain course" coming soon - there's a billboard to that effect in the Jurassic Park section between the underwater tubes.