We bought the combo ticket for Palatine Hill and the Colosseum and visited the Hill first. We enjoyed the Hill as it had loads of ancient ruins lying around for us to look through and under and around. As usual, bring your own guidebook 'cause there's nothing there to tell you what's what. There are: a grotto, a garden, great views of the surrounds (the Forum, the Colosseum, and Circus Maximus) and the city (you can see St. Peter's Basilica in the distance). There are marble bits lying around, so you can take a rest on a marble column if you're tired. There's a small museum with more interesting bits on show (statues, wall paintings) and it's a great place to cool off from the hot sun. (It's also got a lavatory.) Behind that is the Circus Maximus which is now mostly a grassy area bounded by parked cars.
We liked Palatine Hill, mostly because there's lots of open spaces for kids to run around in, lots of trees, and because of terrific views of Rome around you. In reality, there's actually more to see at Palatine Hill than the Colosseum -- don't miss it!
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.