Halo is one of my favorite games of all time, and I played the shit out of the first one when it came out. It was absolutely game changing for console shooters. Before that, I hada SNES (skipped N64 era). It absolutely blew my mind.
Unfortunately, I don't think it really held up. If you played it back then, the nostalgia still hits hard and that's fun. But if you play it for the first time now, it just won't hit the same, unfortunately.