My parents got divorced during the PS2/Xbox era. I took my PS2 to my moms house and my dad must have thought I needed something to do at his house because he took me to gamestop and bought me an Xbox. We asked the guy there if there was any particular Xbox game we should get to go with it, and he was like "Duh, HALO!" Took it home and played it and my dad who has zero interest in video games was watching at it and saying how impressive it looked for a video game.
My and my friends used to have a thing where 6+ of us would get together and hook up two Xbox's and play multiplayer team games with two couches back to back in the middle of the room so each team was facing opposite directions and thus could not screen peak. We'd all chip in $5 and order pizza. Some of the best kid memories came from Halo.
Aside from any nostalgia though, you should play Halo 1 campaign on legendary. There is a reason it's still held in such high praise. The AI is really fun to play with and it always feels like you're fighting against enemies that have an equal or better combat ability as the player which makes progressing feel really rewarding and authentic, without getting too hard or frustrating. I think to this day I can't think of a game that got single player AI right more so than Halo 1. I also think 1 is by far the best in the series. Everything after that is just trying to recapture the magic of Halo 1, not that they're bad, they just never hit as hard as 1 does. I honestly think even today a new player would really enjoy Halo 1. It just gets so much right, far more than most games today do.