We stayed here for a 3 nights over a weekend in January (booked via expedia). I had requested a smoking room in my booking, but this hadn't been passed on - but the receptionist changed it without a problem.

The room was big enough for a city hotel, with loads of space to hang the clothes we needed. The bed(s) were big, clean and comfortable (though only 1 spare pillow). I think the hotel should invest in some new towels though - the towels were small, and getting thin.

The 2 x beers + 2 x waters in the room each day was nice (though one day it wasn't restocked, but this was very quickly sorted out by reception). The hotel bar was small, but nice - and the barman friendly. The receptionist also assisted us in making a reservation at a local restaurant (Henne - excellent chicken!).

There's a u-bahn stop (Märkisches Museum) right outside the hotel. Also across the small bridge, there's a supermarket - great fresh pastries and coffee (though, I think it's closed on a Sunday).

Overall - we enjoyed our stay in the Derag Hotel Grosser Kurfuerst.

lovely hotel, clean room, nice bathroom, friendly reception staff, U-Bahn stop just outside hotel door, 10min walk to alexanderplatz. perfect location and good value for money - would recommend :)

This hotel was clean, convenient, quiet and comfortable. Even if my room was in the second floor facing to the street, I slept extremely well and I didn't hear any noise from the street.
Locating on the side of the busiest center of Berlin, it was easy to either take a public transportation or walk to Alexanderplatz. U-bahn station is 30m away from the hotel door and some bus lines are also riding nearby.
I took the hotel's breakfast and it had wide variety of different type of bread, eggs, cereals, juices, yogurts, cold cuts, cheese, fruits and sweets and even Nespresso machine for coffee lovers.
Hotel allows you to use one hour per day their internet (and PC in the lobby) for free.

We went here for new year's eve 2011/2012 and we were overall very happy about our stay. The hotel has a great location in walking distance, a short walk from both Museumsinsel and Alexanderplatz. Also, there is an entrance to the U2 subway line directly next to the hotel. The hotel itself is clean and nice, and the staff is very helpful and welcoming.
I never tried the breakfast in the hotel, as it was ridiculously overpriced: 16€ in a city where you can have a great breakfast in a restaurant for less than half? Come on!
It is also my opinion that in 2011 (now 2012) free unlimited WiFi in the rooms should be an obvious comfort. In this hotel we got one hour per day for free and then we would have to pay. This should usually be enough, except that with the login-system in the hotel I never managed to spread the one-hour access over several 5-minute periods, and we could only use one device at a time. Too much hazzle when all we wanted was to check if we had new mail and maybe set a new facebook status for five minutes using our smartphones.
Our room was spacious and clean and there were lots of room to put our clothes on hangers. The bed and the pillow were way too soft for my futon-trained back, I had the feeling of being in a hammock! That's unfortunately the way many hotel beds are. We did sleep well though, unbothered by light or noice, even when we went to sleep around 5am on new year's eve.