YMMV and everyone's experience is different.
M1 I coasted, went to class, got home between 2-6 depending on the day, studied for an hour or two and then would chill. Would cram the weekend before tests and was always around average other than one or two tests. M2 was literally hell. I'd study the way I wanted/the way I actually learned best and would fail the midterms, sometimes would be failing even after the curves, then be miserable for the next week or two and do well on the finals just to pass. What sucked was I was studying a TON for both tests (12+ hour days every day) just to pass. The irony was my highest section on level 1 was pathology, the test I'd always fail, and I did pretty bad on the stuff for tests from M2 I did well on.
M3 was a breath of fresh air. Finally got to be in the clinic and crushed it compared to pre-clinical years. It actually felt like I was doing something relevant to my career even if the pre-clinical knowledge was necessary. M4 was also awesome. Sub-i's were a ton of fun for me and I really thrived at that point. Once interview season hit rotations were really chill and I actually managed to set my schedule up so I only worked 4 weeks during a 12 week period (EM + hospitalist rotation with 2 weeks off for interviews in between each). After that it was all downhill until residency.
Finishing up intern year and it's been hit or miss. Start of it was really rough because of family stuff, but once that was under control it's been awesome. Way better than med school imo since I'm actually in the field I want to be in and not having to deal with rotations/material that bored me. Some rotations suck, but overall doesn't even compare. Plus I'm getting paid now, which is really nice, lol.
Would I do it again? Probably, but I'd definitely tell pre-med me to get ready for some serious periods of misery.