We enjoyed our experience at Deniz Houses. It is a small hotel tucked away at the end of a street. Location was perfect for us. We explored the nearby sights the first day and ventured out further during the following ones. Distances to the sights are slightly longer than mentioned in the listing. (Suggestion: have a city map for the guests to take. I wouldn't mind paying for it.)

The men working at the reception desk were very friendly, willing to help and ready with an advice.

Our room was fairly small, compared to the small hotel rooms in the US, but it was enough for what we needed it for: sleep and get ready for the day's adventures. We had four suitcases with us and had enough room to walk around, which was my concern before getting there. The room looked like it does in one of the pictures, but was quite smaller in reality. It was clean. Having bottled water in the fridge was nice for having arrived very late at night. I saw a couple of other rooms on our floor and one seemed smaller (probably wouldn't fit our four suitcases), the other had three beds and was very roomy, with a view of the sea.
When choosing hotels, I'm firstly concerned with cleanliness and safety of the location. These criteria were met, and for $40/night!

Lastly, the breakfast and the terrace. Both enjoyable. You walk up a windy staircase to the fourth floor for breakfast. We wished for more day-to-day variety of food, but there was enough to choose from. It sure beats the cheap US hotels: potatoes au gratin, sausage, warm savory pastry, yogurt, jams, honey, dry cereal, three different kinds of olives, about three kinds of cheeses, breads, fruit, dried figs, desert, coffee and delicious Turkish tea. Couldn't complain. The view from the terrace was breathtaking (for someone who's never been to Istanbul): the Sea of Marmara on one side, some of the city and the Blue Mosque on the other sides.

Minor inconvenience: not enough outlets in the room, even to charge the basics like phones and a camera. We used the ones in the bathroom.

My biggest gripe (and confusion) is the fee for the airport transfer. ‎€25 one way seemed like a ridiculously huge amount of money to pay for the distance (20 min. ride). Sure, it saves you time arranging the transportation for yourself, but I wish we put in more effort and found a cheaper way. It may be worth checking out the taxis that are in abundance on the same street.

Overall, a good experience. Thanks to Kamil and especially his crew!