We did not stay on "The Level" so this is our experience as guests staying in a normal room.
It is exactly what you expect from a hotel--a clean room, plenty of toiletries, competent staff. The bed was actually quite large and the concierge is helpful, but this alone does not justify its expensive price tag, though. So if you are not enjoying the sights or if you are trying to save money, I would not recommend this hotel.
If you are sightseeing, Melia Berlin's location is unbeatable. It is no more than a 20 minute walk from everything (Brandenburg Gate, Museum Island, Reichstag, Check Point Charlie, Topography of Terror) and for everything else the metro station is LITERALLY outside the door.
Its biggest drawback: expensive WiFi. I thought that we would be able to go without WiFi, but that proved difficult--the need to look up directions, sights, restaurants, opening times, etc. made the lack of WiFi painful.
Have the money? Splurge on the hotel. Trying to save a buck? Try to find another hotel with a great location because this isn't the only one.