Stayed in Senatus hotel for 3 nights for a leisure trip to Istanbul. As it was already mentioned location is very central, close to all possible old city attractions and sight seeings. Staff is very helpful and nice. I have ordered transfer service from IST airport to the hotel, but they due to some reasons didn't get there, so hotel asked me to take a cab and they paid for it upon arrival to the hotel.
Again all the facts about amenities in the rooms are true, everything is clean and well prepared, bottle of water, tea and coffee in the room are complimentary. Breakfast is a bit unusual for European taste, but your are in Turkey after all so have fun and enjoy (and they provide not just local dishes, so not a problem at all). Bed is very soft and comfortable.
In case you are interested in having excursions or boat/bus tours staff will help you with the options and arrangements.
There are only 3 things i could consider as minuses for this otherwise perfect hotel:
1. Booking.com says that hotel has WiFi coverage in all hotel areas - that is not completely true. Good WiFi is only in the lobby, restaurant and i believe on the 1st/2nd floors. My room was on the 4th floor and I been constantly searching for a right location to get signal and anyway it was very poor.
2. Noise - if your room has windows on the front side it might be very noisy in the evening;
3. Door to the bathroom is actually transparent, so if you are not alone or staying with someone with whom you are not completely happy to share your naked appearance it might be a challenge ;)
But in principle i am very happy with a hotel and definitely would recommend it!