"How much you remember" from your medical school classes is not so much of an issue as "how much did you learn in the first place". Anything that you do not use regularly will become a part of distant memory as long as you learned it in the first place. Is this a problem? No, because if something is in your distant or long-term memory, you can recall it with review.
You are going to find that when you begin to review for USMLE Step I at the end of your second year, it is far easier to recall what you have LEARNED in the first place then to try to do a major learning feat at this time. This is why daily review and systematic mastery of your coursework makes REVIEW so much easier amd the last-minute "exam cram" is counter-productive and contributes more to test anxiety than actual mastery.
Things that you use daily, you tend to remember and recall easily. When you need to recall material from your first year coursework during second year, a brief review will help you accomplish this. When you need to recall the pathological principles of your patient's disease process, you may need to review some of your pathology notes or a pathology text during third year.
As a surgical intern reviewing for ABSITE (American Board of Surgery In-Training Exam), I found myself consulting some of my review books for Biochemistry and Pathology. The important thing was not so much that I could actually remember some of those little facts and factoids from my medical school classes but that I could reveiw, recall and enhance them with my knowledge acquired since taking those courses.
I had no difficulty walking into the Gross Anatomy lab on the day of my first lab practical and identifying the structures tagged by my instructors at the time. If I had to do the same thing today without a review, I would likely not do as well on that test. With a bit of review (would take less time than learning all of those structures in the first place), I would likely do better than my first lab practical because I now have the added experience of four years of surgical residency.
Bottom line: You will do something of a "data dump" at the end of each or your classes. This is not something to be too concerned about because you are going to get ample time to revisit your "dumped" subject matter when you review for boards. You are also going to continue to build upon your knowledge foundatation as you move through medical school, into residency and into practice. If you have diligently studied and learned your material in the first place, a review is all you are going to need for recall.