If I were planing to take the new version, then I'd start by looking at everything that AAMC has released. The biggest problem is that the booklet they released talking about the new exam has not changed in nearly three years. The latest release (April 2014) is not much different from what they had as a free download in Fall 2011. The sample passages and questions they released in that book feel different than current passages and questions, but not drastically so. The strangest thing is how they have divided and mixed topics. Organic chemistry has been split across physical sciences and biological sciences. Some physics topics have been removed and others de-emphasized. General chemistry doesn't seem to have changed that much. Biology has expanded, especially in the area of biochemistry. I do believe they've trimmed the fat and will focus on topics that have relevance to medicine. But the reality still remains that they have not updated their sample materials in a long time. This can only mean that they are still in the process of retooling their materials. If you do the math in terms of how many passages they are going to need come Spring of 2015, then you have to figure that they are in a bit of a panic trying to write, scrutinize, analyze, and modify passages in time for the new exam date. It's going to be a work in progress.
With that in mind, I personally think it's insane that anyone would purchase materials now for an exam that no one has seen before. They were written over a year before the exam is set to change. The last time there was a major change to the MCAT, in 1991, the prep materials played catch-up for several years. It wasn't until maybe 1995 that the practice materials available became abundant enough for someone to thoroughly prepare. The trajectory right now seems similar to what it was like in 1990, only without the prevalence of the internet.
What I have been telling people planning to take the new MCAT in 2015 is that their exam is at the earliest nine months away and no one has seen it yet, so they need to relax and focus more on having the subject matter covered than to start preparing for the exam. Start with the
AAMC guide and learn what is tested. Some of the current preparation materials (to be honest, the more detailed ones) will remain highly relevant when you look carefully at what they are doing. This is especially true in biological sciences. The test is going to get harder and require more review, but as always, test taking skills will be paramount to doing well. The behavioral subjects add an extra layer of material that must be reviewed, which will increase the average person's total preparation time. But if you look at AAMC's practice materials, the new section will be very similar to current biological sciences passages that are based on experiments. You will need to interpret data and analyze the passage using common research ideology, and if you understand the basics of research theory, then you can get many questions correct without completely understanding the experiment in the passage. Knowing the content and being familiar with terminology will certainly help, but being good at interpreting experiments and test taking will pay dividends more than memorizing facts and historical events in psychology, sociology, and neuroanatomy.
For biological sciences, test writers appear to now have carte blanche to go into as much detail and incorporate as much outside information as they wish. If you read what AAMC has been saying for some time, then you'll see that they want to emphasize coursework material. If you are going to start reviewing now for the science sections, you will need to go into depth in biology while mastering the basic concepts in organic chemistry, general chemistry, and physics and then emphasize examples where those subjects apply to bodily functions. Periodic motion just became the lung and heart more than springs and pendula, although you have to fundamentally understand springs and pendula to answer questions. No one knows how well the test writers will follow AAMC guidelines, but if the practice passages are any indication, it will be more information heavy and experiment focused.
Although I do not speak on behalf of BR, I fully agree with their decision to refrain from releasing materials for the 2015 exam until later. From a business perspective, it's crazy to not rush to put stuff out now, because students will blindly purchase whatever is available. It's a business no-brainer to start releasing material now if you want to cash in. But as many of the complaints about BR have pointed out over the years, we don't really follow traditional business practices. Expect to see materials from BR in late November at the earliest, and expect several different editions over the first few years of the new MCAT. It's what we did from 1990 to 1995, and old habits seem to resurface when the right situation presents itself.