We stayed for 3 nights over Christmas, using a suite upgrade (Regency Suite King).
Overall it was a very nice hotel, though I agree it is starting to look dated. We were previously at the PH Vendome in Paris, so it is hard to compare any other hotel to that one.
That said, we were pleased, and attribute some of the shortcomings we found to the short/changed staff over the holiday. I'm sure it is among the very nicest of hotels in Cologne, though we didn't go into any others.
Our suite was very nice, overlooking the river and Dom from both living room and bedroom - that view is just as nice as they show on the website. And we were thrilled to find they had put a small live Christmas tree in the living room - it was a very very nice touch because we were there with our 2 kids, so Santa had a place to leave their gifts.
RC was closed for breakfast so we ate in the restaurant, which was a pretty good buffet.
RC had coffee all the time, and snacks in the afternoon and evening hors doevres and cocktails. It was a strange club - it's in the open area of the 6th floor rather than a separate room, and I found it odd that no one ever checked access to it. The evening food was not great, but it was a nice RC overall, and worked well for us.
Location is great, a quick walk over the bridge to town.
I would definitely stay there again if I was going back to Cologne.