I'm an M4 now. The past 3+ years have definitely been the best in my life. No ragrets whatsoever about choosing this path.
For pretty much the entire first 2 years I felt like I was at summer camp.
M3 started to get a little grindy but it was really gratifying to be making progress towards being an actual doctor. I remember my first rotation on family medicine I was completely useless in every respect. By the end of that rotation I could kind of put an H+P together... By the end of M3 I was calling consults, seeing patients in clinic on my own and presenting a (sometimes halfway decent) plan to the attending and writing a note afterwards.
Now as an M4 in the thick of subi's / step 2 / ERAS / etc, I'm feeling a little burnt out and tired of saying "Hi my name is Gurby, I'm a medical student...". I'm jealous of seeing the interns working so hard, learning so much, improving so insanely quickly. I feel like I'm ready to jump into the pool and start really learning to swim, but I still have another year of writing pretend progress notes. I'm sure intern year will be here before I know it, and I'll be looking back at how easy I had it in M4 and will be wishing I relished this time more.
Try to enjoy every step of the process and don't be too focused on the light at the end of the tunnel. It's a looonnnng tunnel!