I can't really review this site as I went on a Monday. FYI: The site is closed Mondays as are many other museums in Indonesia. If you plan to visit do it on another day. Bribing the guards didn't work either (to walk the outdoor area).
I also recommend to combine this (not UNESCO) with a visit to : Ceto and Sukuh Temples. You won't be able to visit on a day trip by train; you need a (private) car then.