Very charming beach hotel, in local style, very atmospheric. The best rooms are upstairs ones, especially nb 6 which is their honeymoon suite, very worth it for 95 US; Just don't take one of the new rooms yet (as of summer 2008) as they still smell of concrete.
VERY clean, great staff. Some problems with warm water (sometimes).

Casa del Mar is a charming small hotel on an exquisite stretch of beach with a relaxing untouristy atmosphere. The rooms are spacious and clean with imaginative hand crafted furniture and have individual patio areas. The hotel is set in a lovely garden and screened beach area with comfortable lounge chairs and hammocks. There is no pool, but you can swim at high or low tide. Swimming at low tide was magical. We walked out across flats of shimmering white sand, shallow tidal pools and beds of cultivated seaweed to a vast expanse of white sand and crystal clear turquoise water.
Casa del Mar has a lovely restaurant under a thatched pavilion, with excellent food and service. They do not sell liquor, but they make delicious fruit juices or you can go to the bar of the hotel next door for beer and wine (or plan ahead and byo). They do not object to you bringing it back to consume in their restaurant. There are a couple of small bars along the beach with a definitely laid back atmosphere and fun places to have a drink.
The staff at Casa del Mar were friendly, competent and helpful. They arranged the airport transfers and a snorkeling trip, and indulged my efforts to speak Swahili.
My husband and I loved our stay at Casa del Mar and did not experience any of the problems described in some other reviews. I had been to Zanzibar before and stayed at a larger “luxury” resort, but preferred the ambience of this hotel. I feel it reflects a philosophy of low-impact tourism and respect for the local community.

We traveled to Zanzibar after a safari and a trip to Mt Kenya, so we where looking for a place to relax and sunbath.

A friend recommended Hotel Casa Del Mar, in Jambiani, and we where not disappointed! The hotel has a friendly and calm atmosphere, and a great staff. Our room had a balcony with a sea view and the hotel lies more or less on a wonderful white beach. The restaurant serves very good food, and we ate almost every meal there. Jambiani is a very calm place, and although it was high season when we where there, the place is not crowded with tourists.

Last review is spot on - except its getting worse...
Drains still smell dreadful, there was no hot water at all in one of the buildings and none in ours either the first night.
Staff are still sullen, food isn't good - and if it isn't on the limited menu they can't do it [like frying eggs on both sides].
No alcohol is sold because it migt upset the villagers - but you can walk up the beach and buy beer or wine from one of the same villagers..
Upper floor rooms have very steep stairs [think stepladder with no railing] up to bedroom and power goes out frequently - coming down in the night in pitch darkness to use the bathroom would be an interesting experience.
Neighbours have almost finished building, but now stand on their balcony and stare at guests.
And did I mention the sand flies in the seaweed ?

Security is a real issue - beach people are allowed onto the property all day and hassle guests relentlessly trying to sell shells or beach sarongs or massages or scuba diving, and unless you lock the shutters the downstairs rooms are wide open [there are no safes].
Villagers on the beach not actually trying to sell you anything are a lot less than friendly - Jambiani is a very poor, very strict Muslim village and comparatively rich swimsuit clad westerners really aren't welcome. We were shouted at to go back to the hotel when we didn't buy anything, and trying to take a picture of the almost empty beach incurred screamed abuse from everyone behind us who couldn't possibly be in the shot.
Really didn't feel safe - have done lots of travel in deeply Muslim countries like Pakistan & Syria and have never felt hostility like this, and Zanzibar has a history of killing foreigners in its violent revolutions [12,000 in Stonetown in 1964 - see Rough Guide].
Very happy to leave after one night