I'll start with the easier question first. The facilities are quite good. The classrooms are bright, roomy, have lots of visual aides, posters, etc. They use smartboards, which my kids really like. They have a large sports hall, and sports is actually an area they seem to emphasize a lot. My kids like that as well. As far as I know there is no functioning swimming pool yet, though I understand it is in the works. There is a program of extracurricular activities, and it is going to be expanded further in January.
As for the harder question, are my kids happy? I would say most of the time they seem to be; one of them seems to be having more fun than the other. The school emphasizes discipline and tradition, which (in theory) should not necesserily mean no fun, but I'm not sure how that works in reality. My experiences with trying to communicate with the school has been very positive; I always get responses to my emails, which is a good sign.
Hope this is helpful in any way. Do you have kids at sherborne?