There are a few personal reasons why Chamber of the X-Men is one of my favorite superheroes to do this day, and I want to get those out of the way before I talk about what Chamber stands for as a character.
To begin with, Generation X was a great comic from the 90s written by the pretty-much-always amazing Scott Lobdell. (Bachelo deserves a lot of credit for his artwork, and I don't want to leave him out, but for our purposes, Lobdell is the important one.) Lobdell's work was perfect for a book like this, because it never built on any overarching story throughout the entire series. There were small vignettes revolving around occurrences with the team, but mainly, each incident was an excuse to get the know the characters better. At this book's very best, roughly 2 years go by without any real action happening, but tons of character development.
Not only is this a character-centric book, it was also a book about a team of teenaged superheroes, and in that situation, you need someone to identify with. Arguably, this role was filled by Banshee, team leader and headmaster, and Chamber. So right off the bat, a reader of Generation X was drawn to this character.
Personally, Chamber resonated with me for a few more reasons. One, because he was openly into rock metal music and wasn't shy about it, wearing leather jackets and all black pretty much every time he's drawn, even to this day. Two, he played a "grumpy outsider" type of role and didn't fit in with the rest of the teenagers on the team. I think we felt like we were outsiders when we were teenagers, but Chamber was an outsider twice removed -- Not only did he not fit in with society, but he didn't even fit in with the other teenaged mutants. It was hard not to sympathize and empathize with him.
More importantly, and the reason why Chamber still stands out in my mind as a great superhero today is that his mutant power exemplifies loss.
The X-Men teams as a whole are about not only forgiving someone who has wronged you, but working for their benefit. They are shunned and hated by the world at large, and yet still make every effort to ensure its safety. (Imagine for a second you run into someone who has wronged you, and they ask you if they can have a dollar for a coke. Would you give it to them?) Not only are the X-Men fighting for the sake of people who hate them, but they often suffer deep physical and emotional scars because of their mutations. This is where I think Chamber stands out the most.
For one, Chamber's mutation didn't manifest itself until he was well into his teens. This is crucial because whereas some mutations are born with their physical mutations and the rest acquire them around puberty, Chamber had the chance to become pretty much a fully formed human being before his powers appeared. The kid lost a lot more time than most mutants.
Also, similar to Rogue, the manifestation of Chamber's powers hurt someone he cared about. His chest explodes in a ball of fire, and he cripples his girlfriend for life. They never reconcile or get back together.
Similar to Nightcrawler, his mutation is somewhat terrifying and arguably grotesque. It depends on the artist, but sometimes (like the image above) you can see that he has flaps of burnt skin hanging off of his face. But what makes him most unique is that his mutant powers emphasize the extreme loss that has received.
Nightcrawler's mutation appears as a tail, elf ears, blue fur and weird hands and feet. Angel's physical mutation is wings on his back. Marrow has bones popping out of her skin. Anole takes the form of a...lizard thing. Rockslide is a giant rock monster. Out of all the mutants with physical mutations, Chamber is the only one who is just missing something, and the thing that he is missing is half his face and the entire core of his body. Even his superhero code name is just "empty room". This is an avalanche of symbolism.
In terms of the mutant lottery, it seems that Chamber is absolute dead last, losing all his personal relationships that he built up in his teenage years, losing his face, voice and chest, and having just a big empty hole inside of himself. And yet.
And yet Chamber, like all the X-Men, works though his mutation to fight for people that hate him. Not only that, he is currently a teacher at the X-Men school, giving back to teenagers who need his help the most. Again, this appeals me to personally as well. Being a teacher and knowing a lot of teachers, I can attest to the fact that the best teachers were usually the worst students. I like to think that Chamber is the best teacher in that school.