Bagging medical entry tests seems a popular sport at the moment (Predicting med school success is as easy as UCAT, p51, MedObs 13/5/11).
It is understandable that many recently graduated doctors would have unpleasant memories of UCAT, since it is harder and more competitive than other assessments (GAMSAT, year 12 or university exams) and may not have had success in getting into medical school through the UCAT route.
However, UCAT is a better predictor of later professional success than GAMSAT or university marks since it tests generic reasoning skills.
Whatever criteria is used, there will be people missing out and they will criticise the reliability and validity of the test. For a society to progress, meritocracy must be rewarded however it is measured.