Great experience overall. Stayed for almost 4 weeks.
The good—
The room was just as pictured in the listing. The view is really nice. A/C and heating was very good. The shower temperature and water pressure was good. Kitchen has everything you need to cook at home. The bed was firmer than I thought but it was still good enough to sleep/ lay on. Clean pillows, sheets, and comforter. Someone came after 2 weeks to give us fresh linen. Washer/ dryer worked perfectly. There's a vacuum so you can clean up after yourself as needed. Wifi is great as well. The gym in the building is basic, mostly good for cardio and some weight exercises. The restaurant in the building is also good for above-average pricing. Starbucks is a 5 min walk away, I went every day. There's also 5 markets within 5 minute walk for your groceries. Was much more accessible to us than Taksim or Fatih.
Things to note—
I wish there was an outlet by the table. I worked from there every day and had to move to the bed to charge my laptop. The room sometimes smelled bad, maybe due to pipes from waste on other rooms. Also there are a few beggars (children and adults) that hang around the complex due to it's higher-end appearance. Aside from the few restaurants around (there's 3 that were worth it), there's not a lot of eating out options though so be prepared to take a taxi to the Mall of Istanbul or the more touristy areas.
It was our 2nd Airbnb in Istanbul, staying in the city for 6 weeks. We did the touristy stuff for 2 weeks but our Airbnb was not good. In this one I was actually able to work and relax more. If you're staying for long-term, it will be hard to find a better place to stay.