The exams are testing information that you should know after 2 years of pre-clinical curriculum: anatomy, biochem, pathology, physiology, micro, etc. USMLE goes into lots of nit-picky depth and requires its test-takers to dig deep and retain lots of information in order to do well. At this point in your career, anything that has been covered in the first two years of medical school is fair game. USMLE is better written and is more up-to-date. COMLEX is full of "what gas was used in this bioterrorism attack" and "what's this latin medicolegal term" and "what's the name of this worm that infected a kid in a far-flung Pakistani village that you've never heard of." Oh, and "what's the CRI for someone having an MI". When you go into the clinical world, you begin to look at things differently, and Step 2 will reflect more 'clinically-relevant' material.
Also, I'm of the camp that believes that only someone who has taken the exam can critique its content.