We stayed in Dar Zaman for three nights and it was a great experience. The riad itself is beautiful and really well kept. We had the Baignoire room, which was very small but this was fine as we didn't need to be in it much, however if you are staying for longer than 3 nights you might like to chose one of the slightly larger rooms. Breakfast was nice - orange juice, a pastry, pancake, yoghurt, breads and jams, and eggs if wanted. The best thing about the riad though was the incredibly helpful and friendly staff. Hassan sits down with you on arrival and goes through a map, giving advice about where to go and how to get places etc - which as it was our first in Marrakech was invaluable. Not only this but he went out of his way to help us out - for example escorting us to another riad which we could not find (as we decided to stay in Marrakech an extra night and sadly by the time we decided to there was no room left at Dar Zaman).
I would recommend getting Dar Zaman to organise your transfer. It's probably more expensive than just getting a taxi from the airport but I do not know how we would ever have found it without them personally escorting us there! I would also say it may not be the best place to stay if you are on your own and you are not entirely confident- as getting back to the riad can prove very difficult (down what seems like a maze of alleyways!) and it took us quite a few attempts before we learnt it!