I'm very LTTP on Halo, playing the first one right now on game pass and I'm liking it so much, mainly for the gunplay. It's crazy how this game feels so good to play today even for somebody who never touched it before. Also, I love the grenade tossing in this game, they have made for some really cool and funny moments. But what impresses me the most it's the AI, I feel like it's much better than even a lot of modern shooting games. Enemies take cover, move positions, run away, hide, ambush... it's all very dynamic.
Also getting the hang of the warthog. I still feel like it would be nice to have different control options for it but it's ok.
Also, I really prefer to play with the original graphics, it's a much more readable game. With the updated graphics I was also missing on a lot of pick ups and stuff in the beginning.
Music is awesome too, so far, and voice acting is quite good. I'm not somebody that cares too much about story in games but I'm certainly curious to see where the whole thing goes to explain the Halo etc.
In short, I can imagine why people think so fondly of this game when playing it for the first time on the original Xbox, it's really good.