Since its always shoulder to shoulder at the Acropolis, at the Pnyx, it may be serene and hypnotically hot with not a soul around! In that case you will need to to know the following Greek expression: 'Skai O Tzi-tzikas'!
In high summer, you'll be seduced by the incessant droning of the Cycadias beetles in the intense but dry heat. The Greeks have a saying about these harmless droning insects, they call then 'tzitzikas' - Skai O Tzi-tzikas which means "its so hot the tzitzikees have come out". About as profound and insightful as our rhetorical "hot enough for ya?" Its still a handy expression to know. Or at other times of year, like spring or fall, there will be no manifestations of O tzitzikas but the forested area which surrounds the Pnyx will likely bring a welcome, gentle, cool breeze wafting through the pines. There will be bird sign and calling back and forth too.
From here one gets an unimpeded view of the Acropolis and, on a clear day, of the coast of Phaliron and Piraeus to the south. The only better view is from Philopapo's Hill close by, only a short (10 min.) up hill trek.