It is really challenging. The amount of hours of study required to get in to medical school is about 25% of whats required to be successful in Medical School. The volume of information and the level of responsibility is intense. This is an environment that is preparing you for residency. Residency is another difficult task. Expect to be challenged no matter how smart you are. When referring to the information your required to study and the amount of time you have to study it, it is compared to drinking water from a water hose that is set on its maximum output. If you study smart and work hard you will be successful.
Plan on putting everything else in life on the back-burner. You will be studying or in class 70 hours per week for the first 2 years.