I stayed at the hotel during a business retreat of 3 days. The surroundings are beautiful and the service impeccable. The rooms are well decorated with an "out of africa" upmarket look. The food was delicious and the desserts yummy.
I didn't give it 5 stars because of the mosquitoes. There was an invasion during my stay! they were all over the place, we could not sit outside in the evening and in your room make sure you spray inside the mosquito net :)
Karen is quite far from Nairobi city center so make sure you don't have meeting in town. One morning, it tooks us 3 hours to get to a meeting.