I think it is very unique in its game types and over all "feel" of the game. Halo Graphix are beautifull, but they are not entirely realistic. There is an Art quality to how they did the graphix. Also it lacks many realistic features like "stray bullets when running" but options that make the game fun because you can shoot and move.
Also its vehicles are a huge advantage, the warthog jumps and moves like it normally would, but can take damage. I have a feeling that Halo for PC will take the PC world by storm. Mainly because those XBOX FREAKS out there(like myself) will all buy it and hype it up, so everyone else will buy it to see what the hype is about.
You are right, it will be a awesome game mainly because of the hype out there for it. If halo had not come out on Xbox first it would have been just another ordanairy game.