The first midnight launch I went to unaccompanied by my parents, the first time I ever had Starbucks in hopes it would help me stay awake, and an absolutely miserable day of high school to follow on complete sleep deprivation and wanting nothing more to go back home and continue playing.
Also, admittedly, the last time I saw Halo as one of the best franchises in gaming. There was a certain disillusionment over the long term about how much different the game turned out compared to pre-release media, including even that long-form playable demo, and also it was one of my first big exposures to the toxicity of online gaming -- it served as one of my personal culture shocks of just how rotten-minded many gamers are, with the constant exposure to just nasty behavior online in that game in particular. There were other games back then that were clear indicators that existed at the time, but I didn't really play on PC back then and Halo 2 served as my first huge foray into online gaming, preceded only by PSO on Dreamcast which I played pretty much exclusively with RL friends.
But that was just my experience with the game, and that's only in hindsight. This very day 15 years ago, I was very excited.