I have children at Charterhouse and do not recognise the criticism. I think it should be acknowledged that all of these schools are pretty demanding in that they require the pupils to work hard, play hard, and to get on with a diverse group of peers. Some find that harder than others, and some are more sensitive than others. At Charterhouse the academic standards are high - much higher than Cranleigh (on a par with Tonbridge, Harrow, Wellington etc), and pupils have to hit the ground running; the support and pastoral care network is, however, marvellous.
Similarly, the sport is taken seriously - the football , hockey, tennis and cricket is outstanding (the u14 cricket team was unbeaten this year, beating Eton, Cranleigh, Harrow, Wellington, Tonbridge etc) with top class coaches and facilities, yet the sport is not the be all and end all in the way it is at other schools; that means that a boy or girl does not have to be in a sporting star to be popular, and there is room for interesting characters.
Charterhouse is going fully co-ed in a few years' time, and will be large with 1000 pupils. This is viewed as a positive step, and has really benefitted other traditional boys public schools. As for the parties, I have not yet seen any evidence that Carthusians party more than other school children, but I guess it is not unusual for a teenager to like a party.
In summary, Charterhouse does what it says on the tin: it is a traditional yet forward thinking 400 year old major public school set in idyllic grounds with amazing facilities. Some people like that, some people don't. The only way to decide is to go and take a look for yourself.