After all the 5 star comments, let me add a few points.
We stayed for 3 nights. Location is perfect, smack in the middle of Palermo. Apt is good sized.
A few things we wished we had know before:
Pics in the listing are professionally taken and show the apt larger than it actually is.
There are only a few tiny windows which look out on a narrow alley which was partly filled with garbage and old matrasses which stayed there during our stay.
Car/parking:
The apt is in the limited traffic zone, which means a 5 euro/day extra charge if the car is used before 8pm (Sunday excluded). Need to get the charge ticket at a shop, activate online etc. A bit cumbersome.
Also: there is no dedicated parking spot. Parking on-premises is on a first-come/served basis. If one arrives after 6pm - good luck - you'll have to start touring Palermo in search of a scarce parking spot on public streets.
The apartment would benefit from 2 extra, comfortable chairs in the living room/kitchen. There's enough space for this, and it would give everyone a decent seat in the evening.
Be prepared for some shouting at night of party-goers/passers-by (to be expected in the middle of the centre).
It would be nice to apply a bit more TLC and repair the support for the shower head. The shower stall is cramped enough that one could do without the complication of holding the shower head in the hand.
Also, there were only 2 bikes available (parked in the hallway of the apt), instead of the 3 promised in the listing.
We did enjoy our stay at this apartment.