My first exposure to X-Men comics was the Dark Phoenix saga, which many consider to be the greatest X-Men story ever told, even to this day. It was like saying, “Oh, you have a passing interest in trying some really light, social drug? Here, try this crack.” Before this story I would read comics occasionally. Really just whenever I would happen to get some. I never actively sought them out. After this story I wanted everything X-Men I could get my grubby little hands on.
I’m not going to get into too much detail on what came before, since a lot of that has been changed retroactively. But essentially Jean Grey aka Marvel Girl, one of the original X-Men, is imbued with the powers of the Phoenix, a cosmic entity capable of great and terrible things. For a while, Jean seemed ok. Her powers of telepathy and telekinesis were raised to an unprecedented degree, but other than that she was still just Jean.