5/5 - Excellent
We went as a day trip with one of the Expedia "Things to Do" - had a great day visiting the Pena Palace, the town of Sintra and stops at a couple of coastal locations on the way back to Lisbon. The Palace is spectacular, but be prepared to do a bit of walking, lots of slopes (small shuttle bus is available within the site but infrequent from what I could see) - views are amazing from the top and you'll be blown away by the architecture - probably as close to a Disney castle as you could get :)