Staying at the NH Berlin Potsdammer Platz was ok if you want a more out of the centre experience. It is a 5 min or so walk from the nearest tube station, just a couple of blocks and you're connected with with the rest of Berlin although depending where you want to be this could become a half hour journey. We didn't particularly want to explore the hotel surroundings as there wasn't much appeal but I believe there is a park further down and plenty of cycle paths (and hire at the hotel).
The hotel staff were friendly and helpful, and the hotel lobby was quite acceptable with breakfast being served within the lobby if you go for B&B.
The room itself was quite basic but clean and comfortable, nothing really to write home about but if you're just sleeping and bathing there it's more than adequate. There is a bonus of free Wifi, you just need to get a new voucher to login from reception every time it expires (up to 24h).
I would consider staying again although I have stayed in more central and nicer hotels in Berlin for the same price.