Lewa is a wonderful experience doing amazing conservation work. We stayed at Lewa Safari camp, which is perhaps lacking a tiny bit of the luxury touches of more well known camps in the Masai Mara, but, the personal touches and knowledgeable guides, combined with the chance to see black and white rhinos AND Grevy's zebras is just amazing.
The camp also has a strict two-vehicle near animals policy -- such a nice change from the Mara, which can feel like a circus when 8 cars line up near a lion. We felt as though we had the place almost to ourselves, rarely seeing other vehicles during our safaris, and this was at the height of the season.
Much of the money you spend here also goes to the conservancy, which is an added bonus to staying here as well. I highly recommend this experience. You see amazing animals and a great conservation effort in northern Kenya.