First, the excellent points about the apartment - the location and the decor. The location is perfect and the decor is beautiful - simple and elegant. The view is lovely from the living room, a charming old city view. The bedroom looks out onto grey internal building walls, but that isn’t a big deal to most, it wasn’t to me. Water pressure is also excellent.
There is a ton of storage space, because it doesn’t appear that anyone lives there, so it’s a great choice for a long term stay, as long as you don’t mind cleaning the apartment yourself, as no cleaning service is offered.
A potential downside of no one living there is that you won’t find the small welcome package you often see, with recommendations of restaurants or local things to do, but it’s easy enough to figure that out for yourself, especially in that area. A larger downside is that the apartment could use a bit of love - small broken things that someone living there would immediately notice and take care of. The owner is very clear that he doesn’t live locally, although he does have an assistant who gets you the keys and shows you around the apartment.
All in, I would recommend staying there, with one caveat. You have to be ok with second hand smoke. Geneva is a big smoking city generally, so it’s no surprise, but it can get unpleasant from people standing outside the building, or sitting at the beautiful little fountain right outside it and smoking. In good weather, it’s constant. In the rain, they stand under the awning under the living room windows and smoke. It’s just a part of staying at an apartment in old town Geneva, and there is an air purifier in the apartment, which helps a bit, but it can be unpleasant if you’re not used to it. Any apartment in the old town might have this issue, depending on what the windows look out onto and how close to the street and cafés it is, so it is worth considering generally.