The apartment is in a great location just steps away from the city center of Monastraki square. There is a great view of the Acropolis from the front balcony, the apartment has a ton of space (though the bathroom is very small), and it's nicely air conditioned. The building seemed safe and secure, though the back staircase to go up to the apartment is a bit dark and grungy.
One point of confusion was that the apartment comes with 4 or 5 keys and it wasn't clear which key goes with which door (the owner provided numbers for the keys but it was still confusing). There is a specific key to open the elevator door and if you don't know which one it is you may feel like you're getting stuck in there for a few minutes (it's a tiny single person elevator and it gets hot in there quickly). We avoided using the elevator after this.
The only other issue was that after a long day of exploring the city we came back the place to have no hot water for showers. The owner left instructions for how to turn the water heater on, and we followed them then waited 20 minutes, and still no hot water.
Overall we enjoyed our stay. The apartment was priced at an average value (so not a great value but could've been worse I guess).