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.