For some context: I got hooked on HPMoR because of its humor in the early chapters, and some then-mind-blowing characters, ideas and plot twists in the first half. That's how I ended up on this forum way back when. However, the story has gotten darker, more preachy and short on comic relief in the last half. This is pretty standard for multi-volume works and is probably intentional, but I still miss Comed-tea, soul-eating Tracey and frolicking woodland creatures.

HPMoR is "more than just a decent read" because it is a well-designed and successfully implemented device to gently introduce new people to the ideas of rationality and transhumanism. In that it is similar to what Atlas Shrugged did for Objectivism. It also helps that the story has no obvious plot holes and idiot balls.

Some people change their life-pattern after reading HPMoR. Why?

Probably after lurking or participating here, not just after HPMoR.