I stayed at the Hotel Kaiser for 4 nights in June, for a conference in ICC, booked through hotel.com for 48 euro per night. The hotel was really great for that price. A 15 minute walk form ICC 10 if you step up a little) through a little park along the Lietsenzee. And easy to reach from Tegel airport as well, simply take bus 109, which goes every 10 minutes and get off at Bismarckstrasse x Kaiser Friedrich strasse. From there it’s a 5 minute walk to the hotel.
The entrance to the hotel is not overly marked, but if you keep the street name and number at hand, it will be easy enough to find. You ring the bell, the door will be opened, you enter a hall and at the end on the left-hand side you’ll find the decorated elevator. I thought it looked very hippie-like, but the hotel was very decent.
The room was adequate, with a lovely huge window and sun coming in in the afternoon (room 31). The hotel covers 2 floors in the building and as the floors are wooden, you’re bound to hear stumbling from upstairs neighbours if you’re on the lower floor. I was on the top floor and though walls were a bit thin, I slept well. Beds are bunk-like solid, which is the way I like it, but it may not be for everybody. Pillows are thin as well.
There was no safe in the room, but you will find a bible and a big tv. I didn’t check what channels were available, probably all German anyway.
Wifi was fairly good. It disappeared on me for a few hours, but then it came back again.
Staff was very friendly. Mostly young Russians women, so don’t expect long conversations in English. But they were helpful and kind.
Breakfast was absolutely super! Warm snacks, sausages, eggs, fruit, yoghurt…etc etc. Check out my photos for details. The breakfast room was very cosy.
Underneath the hotel is a nice-looking pizzeria. I didn’t get a chance to check it out, but I would have liked to.
Subway will get you to the center in about 25 minutes.

We had difficulty finding the hotel as well - as a marker, remember it is close to the Sophie-Charlotte-Platz U station (not the one named Kaiserdamm which is the next stop). It's about two or three stops after Zoo Garten which seemed to be a main stop. The distance from the U made it very convenient to go in and out of the city center, but if you go out, it'll probably be best to prepare for a day's trip, not one from which you can come and go. If you're looking for a significant nightlife, though, this is not the place for you. There are, however, a few restaurants nearby and two internet cafes on the way to the subway.

Really nice big room with big windows and very clean, although it's no frills, so keep that in mind if that is important to you. The staff was nice as well and I was surprised at how quiet it was despite being so close to a main road. Overall, can't complain about this place.

Booked via the Berlin tourist board.

Good location in the old West. In spite of being on the Kaiserdamm (a six lane boulevard) we didn't find it noisy.

A rather good three-star room, comfortably fitted with o.k.-lookig, no-frills modern furniture. We had a very large room, but that might have been luck because we saw that most other rooms were half the size. Or maybe we paid for this, I didn't check it the smaller rooms were cheaper.

The entrance of the hotel is difficult to find, it is also the entrance of the apartment building into which the hotel is integrated. You have to take an elevator to the sixth floor where the reception is (the rooms are only on floors five and six in this large block).

Taxi drivers from TXL (or any other airport) will not know the hotel. If you tell them that the hotel is on the north side of Kaiserdamm and that it is near the U-Bahn (tube, underground, metro) station "Sophie-Charlotte" they will find it immediately.