Pretty central, less than 5 mins walk to Tivoli, Central Station and city tour bus routes. Two blocks away from the Planetarium. Also a short 10-15 min walk to the central area of town with high-streets, shopping, restaurants etc.
The apartment was in new condition, well kept, spacious and nicely distributed. Check-in and communication was excellent, no complaints overall.
The catch is (maybe an advantage for some!), it's a block away from the red light district, so there is some dodgy movement. Also, the restaurants immediately surrounding are generally not of high quality, even though there seems to be many. That changes a few blocks towards the centre.
For non-family travellers, I'd say it's perfectly fine. For those with kids (slow movers), for example, where you are more exposed to pickpockets you need to keep a watchful eye. I left a luxury rental car parked on the street and did not feel it was in great danger, it's more about the opportunistic sort of people you may come across.