In all the talk of graphical downgrades no one seems much preoccupied with 'why?'. Why build something and then proceed to tear it down, piece by piece, in the hope that ever more diminished expectations about the final product won't be severe enough to...
Well pray that your computer has thousands of dollars put into it. Also I will begin using more grades for this game.
Story: You are Master Cheif [stupid name, but kick ass cyborg] who is fighting the Covenant with the Marines and in the middle "the flood" is released and you need to kill an entire planet.
Gameplay: Great since it is Halo with a keyboard, but if you have a weak computer tou will get 20 FPS at times. The AI is smart and will dodge you using several weapons and work as a team. And your marines [if you have them that is] will follow you and use great stratgey.
Controls: Being able to make your own really helps make Halo better for those who have controlers. And a mouse is a far better aiming tool than a analog stick.
Graphics: That depends if you are using a high end PC or a hand me down Windows 98 [me :( ]. The graphics can be barely under the X Box one to looking like a good N64 or a bad PS2 game with horrendous Frame rate.
D or B+
Multiplayer: Great, you can play online with 2 new weapons. The hunter cannon also used by Grunts later in the game and a flamethrower. You also got a lot of levels [but most just go to blood gulch] but sadly lag can plague you. no matter how good your PC is.
Replayability: Good, you have multiplayer and a fun single player mode. But when the game slows down you may want to fling the disc out a window.
Overall: A good port but the high end requirements of this age screw it hard.