This was the highlight of my trip to D.F. It's a little bit touristy with everyone climbing the pyramids and people selling bric-a-brac. However, the experience here is much more tangible than going to a museum where everything is behind glass.
The pyramids are a sight to behold, and they're difficult to climb. The view from the top of the Pyramid of the Sun is worth the climb, but we had a large crowd up there which killed the vibe. All of the smaller/less popular areas were more rewarding, IMO.