An impressive museum just opposite the Acropolis. The most impressive feature is that the whole museum has been built above some ancient findings. The yard is made of glass and visitors can actually walk on this glass floor and see the findings beneath. The absolute sense of walking in the air!
The interior has three floors and lots interesting exhibits. My favourite was the second floor with the gorgeous and so detailed statues. The third floor hosts the frieze of Parthenon (with copies of the missing parts that are hosted in the British Museum) but it was not as impressive as I expected. Videos were playing in various corners with the history of the Parthenon, the building of the museum, some excavations.
A great thing to do is to have a coffee at the terrace of the museum with view to the Acropolis, but seats are few and visitors are many, so you might seat only if you are lucky enough...
The only bad thing: the exhibits were not efficiently labeled and explained for foreigners. I am Greek and I understand some archaeological terms, but a foreigner might not, so it would be good to explain the exhibit in more words.