I disliked school immensely, the only fun part of it was Theater, but at my HS theater was "geeky", not like Glee or High School Musical makes it out to be (then again, we didn't have musicals). I wanted to be popular but wasn't. I was shy, immensely shy. I went home with bright red blotches on my chest from the difficult time I had with social interaction, even though I'd known these people for years and years. It was rotten.
But I went to my 10 year, and it was OK. People were still bascially the same, and the popular group at my school (which was also the cheer/football people AND the rich people, they were just all the same at my school...you *rarely* had a poor kid who was popular, unless it was a male on the football team...cheer was impossible to break into unless you were already popular/wealthy) was still VERY much in charge. So the "geeks" just sat in the back and made fun of them, as usual, especially when they said that someone who drove a couple hours to get there won for "farthest travel to the reunion" (when I had come from 3 states away).
Went to the 20 year...was so expensive for us, especially given the travel, that hubby couldn't go to the actual event, but that was OK because he and DS stayed in the hotel room and watched Ratatouillie.
The uber-popular people were still hanging on to what they thought they had, but the others were starting to get out from under their grasp. There was a brilliant moment when one of the organizers, who had rented a JUNKY sound system that couldn't be heard, not a peep, if you were 20 or so feet away, started berating the room (most of which couldn't hear her, didn't even know she was speaking) and using f-bombs to tell us to be quiet. Which was no different from how they all treated everyone while they were cheering at football games. It was HIGHLY amusing.
Also fun? The game "who the heck is that?" which was courtesy of someone who had had so much plastic surgery she could only barely be recognized. The best, however, was when the girl I despised most of all (b/c she dated the guy i felt should be mine) shared with my husband, after finding out who he was, during an elevator ride, "all the work" she'd had the need to have done to feel presentable for the reunion.... Oh wonderful day....

(for the record, she looked great, just like in school...it's just that she THOUGHT she had to have all the work done that cracks me up...she felt she was imperfect, just like I had all those years)
At the 20 year I felt like I could talk to anyone, and many people greeted me with smiles and honest curiousity about what I'd been up to, even though we were never friends as teenagers. It was very nice.
Oh, and we also noticed that we had instant recognition for those we had known since elementary school. We started noticing that the bigger groups standing around talking were people who'd *started* school together. Which broke down the clique barriers even more, since the popular kids from each elementary school glommed together in junior/middle school, then that group from junior/middle all became the same in HS. But to go back to the start, that broke everything down. It was absolutely beyond cool.
It's so weird, because I just hated school, but I quite like reunions!
I went to my 5 year one back in 1980 and haven't gone back to any others. Maybe it would be different now that everyone is old

but back then everyone still stuck to their same cliques.
When I was getting ready for my 10 year, my stepmom told me that at the 5 and 10 year reunions, people are still the same. At the 15 year it starts to change, 20 year you can talk to just about anyone if you wish to. And then it gets even better.
So I'd start going, if I were you. You might make some new friends from people you barely knew before.
My husband loves his. He loves to go and brag about how well he's doing and talk, talk, talk about the old days.
Eee, tell him to stop both of those things! No one wants to hear the bragging, and if you are around, and weren't part of the old days, he shouldn't be going on about them with you there. They should be getting to know each other NOW.