Since I studied at the law faculty this review is based on my experiences there.
First some general information about the UzK: The different faculties aren’t on one specific campus, but are all quite near to each other. especially nice is that between the different buildings there are huge grass fields where during summer time almost the whole city sits, relaxes, plays or has a bbq. Also right next to the main Building there is the „kwartier latäng“ where you can find a lot of bars, restaurants and clubs.
Equipment-wise I would say the UzK still needs to improve: a lot of buildings need some work and are rather old fashioned. Out of that reason there is already a lot of construction work happening, to what there will hopefull follow a modern campus!
The organization of your studies works fine via Klips and Ilias. There is a nice support system if you have problems.
The best thing about the university of cologne in m opinion is cologne itself! Cologne has a lot of parks and the Rhine gives it a special summer vibe. Especially during carnival season the city turns into one big party and to experience that is really unique. Also the Cologne people are unique: sometimes harsh, but connected through a big solidarity with their city and its traditions.
I can definitely recommend studying not the nicest city on earth!