In between revisiting Path of Achra(just left early access btw) i have just completed the original Halo: Combat Evolved using Xemu emulator with a gamepad.
Level design is indeed not very good with the Library and it's neverending copypasted corridors and constant hordes of Flood teleporting out of nowhere being the worst offender.
PewPew-ing aliens on the other hand feels great. I love how expressive the Covenant is with Grunts getting batshit scared if you're killing their squadmates or Elites getting angry when you destroy their shields or laughing if they manage to get Master Chief. Also noticed that their AI is smart enough to know how to use any avaliable cover, to flank you or throw a plasma grenade if you're trying to camp them behind a door. Fighting them is a joy.
It's also one of those games where i actually didn't mind having AI companions. With the exception of that mission where you need to protect admiral "i love standing in front of Needlers" Keyes i never felt that marines were a hindrance or anything. Quite the opposite, they were quite helpful in those missions where you're fighting together and i usually tried to keep them alive if i could. I also like how they're doing a little "Hooray!" each time you're jumping on a warthog.
Is it a great game? - Yep, i think it is.
Would i have bought the original XBox in the early 2000s if i could just so i could play Halo? - No, i doubt it.