Room was small, but didn't feel too cramped as a single traveler. On the other hand, there really wasn't a ton of space, though it was used very efficiently. If you are taller than 6ft/183cm you might be too long for the bed if you like to sleep stretched out. I'm 183cm and with the (very surprising) adjustable bed headrest I had to bend my knees, but with the bed flat I just fit.
Hotel location is top notch, less than 10 minutes walking (or one stop on the S-/U-Bahn) from the central, and literally on top of the major Karlsplatz S-/U-Bahn/tram station you can get to anywhere you need easily and quickly.
One of the windows in my room was broken and I couldn't lock it shut, so noise from outside came through (there was some even that had a truck being loaded until about 11pm) which wasn't great, but that was fixed the next day and I had no issues the following night.
Hotel staff was pleasant and very accommodating even with some relatively unusual requests.
Heads up if you plan on arriving early or checking out and leaving your bags there - they bag hold is self service and costs €2/day so make sure you have some cash on you (reception, if open, can provide you with coins)