Like the Colosseum and the Roman Forum, the Acropolis was one of those sites that I just couldn't imagine the vastness of until I saw it. On top of that, red poppies were in full bloom during our visit and the reds of the flowers mixed among the ruins was just incredible. I also loved that you could see the Acropolis from pretty much anywhere in the city, so it was a perfect landmark when we got a bit turned around during our wanders. Similarly, the view of Athens atop the Acropolis was incredible.
Also, don't miss the new Acropolis Museum near the base of the Acropolis. I thought the museum was very well done and I was surprised to learn that many of the statues and ruins were previously colored. In the museum their were awesome recreations of what some of the statues likely looked like in full color. It was so cool. The video showing on the top floor of the museum was also very informative and in English.