It was, perhaps, our good fortune that we chose to visit Frankfurt when the Design Fair was in town. All the 'posh' hotels we tried to book were full, or asking ridiculous prices. The Senator Hotel was conveniently placed for transport links into the centre. The Tram stop was no more than 5 mins away, with trams every 10 minutes during the day and a journey time into the centre of about 15 mins.
The room was basic but clean. The bed was comfortable, the bathroom small but more than adequate and a very powerful shower. Our fear when we arrived, and having read some reviews on Trip Advisor, was that the nearby railway would be noisy. This proved not to be the case, even to the extent that when we opened the window during the night for some air we were not disturbed.
There is a kitchenette in the room use of which, according to the literature, is charged at €19 per day. We chose not to use it for this reason, although we did keep some bottles of water in the fridge.
Apart from checking-in, we neither saw nor needed to speak to any staff during our stay so I cannot comment on the customer service levels.
Overall this hotel served our purposes very well. It would not necessarily be the ideal destination for a romantic treat, but as good value accommodation, it did its job well.