Sergej, I have yet to find a German tourist that will treat a Southern Euorpean with respect or say anything positive about Southern Europe. This is strange as Germans are great tourists in their own country. (My experience with Germans as tourists in Southern Europe goes back 31 years and is as recent as last year.)
There are many sites in Greece. Yes, I saw the Elgin Marbles in London but I also saw a lot of archeaological sites and museums all through Greece. One of the most fascinating is the island of Delos. On the mainland, the Temple of Poseidon, Theatre at Epidaurus, and Delphi are all wonderful. Then to see Corinth and Nafplion is just wonderful. Syntagma Square with the changing of the guards is not the same as at Buckingham Palaca but is still a wonderful stop. Nothing beats the Plaka (if the Greece economy is doing well). I have been Athens when thriving (1980) and doing poorly (1982). More recently, I have been in 2008, 2009, and 2010.
Enjoy Greece and all the World has to offer. Treat all people you meet with respect and they will (usually) do the same.