If you play through it, I strongly suggest you mess around with the difficulty. The game is at its very best, IMO, when you're constantly straddling that thin line between life and death. You've just stuck an elite's face with a plasma grenade, having your shields torn down to within 1/16" of death in the process; ducking around a corner and finding a grunt with a needler he's about to perforate your face with, you bash his skull in and run back around the corner to find the Elite blow up, taking his buddies with him. Repeat.
If you're not dying every once in a while, I don't think you'll be in a position to really enjoy it. Normally this would be an entirely absurd suggestion, but everything about Halo fits this. You die, you drop back in where the last checkpoint was immediately. No "Game over!" or "want to continue (you miserable excuse for a maggot)?" You can consistently experiment, because failure isn't very painful at all, and since you can't create a save of your own, you won't be tempted (as much) to go back and try to find a "more efficient" means of disposing of the baddies in room 7a (if you're that kind of person, like me). The weapon limit also lends itself well to that.
And never forget: (for halo 1 at least) your rifle butt is as important as your ammo clip is as important as your belt of frag and plasma grenades.
Use them all.
