We stayed in Tunza Lodge in December 2012. It is a very nice place. Very well set up on the lakefront with beautiful views. It wasn't bad, but they could do much better.
We tried to e-mail them to make a reservation, but that failed for 1-2 weeks. Showing up helped, and we had the last available room.
It was nice, but the service could also have been much better. We didn't really felt treated like a guest. More 'like we weren't there'. And above that the hut wasn't cleaned for the first 2-3 days, the mosquito nets had holes and the toilet seat was broken. Ok, its Africa, but with western style prices, they have to keep up service. And treating guests like guests costs nothing...
But if you are looking for a relaxing place in Mwanza, try Tunza. It's special (but do try to get a discount!)