*sigh*
Ok, normally I hate these threads, but as a Halo fan myself, I need to contribute a bit to this in order to make people see not all Halo fans are foaming at the mouth.
You said you think the original Halo and Halo 3 are identical. Other than the basic concept of being a "first person shooter" and the same characters and it being a continued story, it is not. At all. And in all honesty, any expert could see that the level design quality and the story (progression and content) is much, much better in the first. Not to mention the Assault Rifle doesn't sound like a fucking pop-gun.
To make sure you realize, I'm an enourmous Halo fan. Read all the books, read the graphic novel, trying to track down all the comics, looking forward to ODST, Reach, the Anime, and if it ever gets made, the movie. But there is something I will openly admit.
Compared to Combat Evolved and 2, Halo 3 sucks. In and of itself, it's a mediocre shooter, but when compared to its prequels, the game just can't hold its own weight. And it's a fucking shame.