I just want to know, is everyone walking around miserably at USNA? That's what people make it out to be
Yes and no. It depends on the person and on the situation.
My plebe year, it started snowing on Veterans Day. There were still piles of snow around the parking lots in March. The football team wasn't great shakes then, so no exaltation over winning games. Academics took up a lot of time. (I'd been used to being able to have homework done before dinner, if not on the long bus ride home from school. That wasn't the case at USNA.)
On the other hand, I ended up on a great sports team (Women's Crew) with peers who knew how to work really hard and also have fun and enjoy themselves. I saw a ton of great plays in the DC area on weekends. I hung out at my sponsors' house with another plebe and a couple upperclassmen (Sponsors are families in the area who bring mids home to their houses on the weekends. It's a nice way to relax, have a family meal, watch some TV or study while laying on a couch. I wish more civilian schools had a similar program.) I was in several extra curricular groups, including faith based groups. I still have friendships with the people I knew at USNA. There were pep rallies, company football games in the fresh fallen snow, silly games of hockey with brooms in the back shaft, company talent show nights, Halloween costume contests, etc. Even after losing football games, our company had fun tailgaters where we hung out at the stadium, grilling and generally enjoying ourselves.
There were incredible opportunities for travel and training over the summers. I had two study tours to Germany (that were mostly paid for by endowments for international studies). I few in Navy training aircraft. I got underway on an LA class submarine. I got to spend a week in Quantico, learning about the Marine Corps. Awesome experiences that very few of my high school classmates had any exposure to.
No, you aren't going to find beer pong in Bancroft or big frat style parties. That doesn't equate, or at least in my case didn't equate, to being miserable all of the time.
On the other hand, time away from USNA is directly related to having satisfactory grades and to not being on restriction for conduct offenses. If you are failing a class, you aren't going to see much time away from the academy (A more recent grad would need to chime in with details. In my time, there were no weekend overnighters if you were unsat. I don't think you could sign up for a voluntary movement order [ex bus trip to The Citadel to watch football] if you were unsat.)
If a significant party scene is what you are after in college, you may be right to look at other options. The exact situation at USNA regarding liberty, civilian clothes, weekends and other privileges and restrictions varies greatly from year to year. It is likely to always be more restrictive than what you will find at a civilian school. That doesn't have to equate to misery, but it is going to be very different than a civilian school.