Crescent is a good school. Cant say anything about Girls Branch, but Boys O Level is (was in my time) very good (and saves you 1 year as others let you complete it in 3 years). It may not have all the bells and whistles offered by other institutes but it still had a lot of things which really mattered in terms of 'Education' and not just getting students to pass their exam.
If you are thinking of pursuing medical career, DO NOT opt for O level. It is virtually impossible getting into top medical colleges even with straight As due to the way the entry test works.
Warning: I left it in 2006 and cant say if things have changed meanwhile.
A PROUD CRESCENTARIAN.