I booked Hotel Klemm for a wedding that unfortunately fell during the European heatwave! Hotel Klemm doesn't have air conditioning and our room on the third floor was regularly 30+ degrees at night. The hotel can't be held responsible for such unusual weather though!
Our room was a little on the cramped side, and the window was at an angle but the blind wasn't, which meant we had to rig something up to stop the daylight from coming through a huge gap in the blind each morning.
Our main bug bear was the lack of receptionist after 10pm. I assumed Klemm would be a very small, boutique-y hotel because of this but it wasn't at all - it was pretty big. When we arrived at 1am to check in, our room key had been left out (all went smoothly there) but they had forgotten to leave out the garage key we had booked. This meant we had to park on the street, but you could only do this until 7am, so my husband and I got 5 hours' sleep before having to wake up, get a key from reception and move the car. We would have expected them to be really sympathetic and apologetic about this but they were extremely blasé about it. They also ask people to not be in the courtyard after 10pm, but this isn't really enforced and because we of course needed to have our windows open, the noise kept us awake later than we would have liked.