We read the excellent reviews and were not disappointed. We had a 2-bed apartment with our kids 14 & 12. We didn't quite know where Sloterdijk was (!) but it's convenient to everywhere, the train is 5 mins max away, there's a Jumbo foodmarket 2 mins away that stocks everything you need, there's a park behind if you need outdoor gym stuff...
The staff are just amazing, nothing is too much - particularly at Reception but equally in Bar 51 where we ate a few times.
We all came away thinking this place is the choice we could have made for a city break. It's not a luxury hotel but you could have breakfast etc. It is a little utilitarian but the beds (as everyone wrote) are really comfy, the basics in tea and coffee are in the room, the gym is well stocked, the games room was loved by our son. For us, on a 2-night stay, it was perfect.
Thanks again.