Otto 3 is very well located if you plan to make sighseeing trips all over Istanbul.
Obviously the pictures from the site are made with a broad lense camera. Don't expect your room to be this spacious.
But in the end, all things considered, if you are looking for a not expensive room to stay, with a very comfortable bed, in a very centrally located area, Otto 3 is a valid option.
Some things could be improved, but personally it did not bother me. I had a good nights rest (the neighbourhoud is quieter than other streets around Taksim), with a nice hot shower, after exhausting sightseeing all over the city. You might have to take some steep slopes to get there, but those are inherent to Istanbul in general.