Pancake flat. I'm a local. You don't get better courses than Valencia. You'll have the odd street that has a slight incline ~0.3% The bridges you'll cross are flat, and the last part of the course is, if anything, downhill. It's a PR course.
The fact it's held at 8:30 means that the temperatures won't hit 60º which is not uncommon to see in December around noon.
Any other questions regarding Valencia, just ask.