The apartment is in a fantastic location: it's easy to walk everywhere, it's close to great restaurants, it's a few minutes from a Safeway and a Trader Joe's, and you can walk to all of the big tourist sites (if you like walking).
The apartment itself is also great. The kitchen is in excellent condition, it was nice to have Netflix since we have a baby and didn't go out in the evenings, the bedroom is large with super soft sheets, the washer/dryer are really convenient, and the bathroom's shower has good water pressure.
We were there during really bad weather and someone (I assume arranged by Mark) came and salted and shoveled the ice from the steps leading to the apartment.
Mark was a very responsive and receptive host; when our pizza accidentally set off the sensitive smoke alarms, he was easy to reach and very patient as we got the smoke detectors sorted out.
The only negative part about our stay was the upstairs neighbor's house party on Friday night that started at 10:00 and went on until 4:00. This, of course, was not Mark's fault, but we would have liked to have earplugs because it was so loud. We found that turning on the dryer and white noise on our phone drowned it out enough so that we could sleep.
That being said, we would stay there again and would absolutely recommend the place for others!