I wouldn't say "much harder." That's such an overused pair of words for the MCAT. I would say it is less straightforward in regards to the AAMC and how the questions are made and more on the line of heavy critical thinking, which is why I take a minute or two longer to finish an ICC passage set. I only did a couple but I found them reasonably challenging and checking my answers by searching all over the web from different sources helped me reenforce some concepts. I still think the most difficult passages are found in the TPR online FLs. For sections, I think the Kaplan Topical and Section PS tests are ridiculously hard. I would say ICC trumps in difficulty in their BS section, with the Kaplan section tests (not the topicals, they are not as hard) coming in as second.