Should they? Definatly. Will they? I doubt it. They said themselves that Halo 3 was the stunning conlclusion to the Halo trilogy. That doesn't make it a hundred percent sure that they won't make a Halo 4. But I think they're going to make different games. Although they would make a lot of money with a Halo 4. But they'd have to come up with another situation for Mastercheif. What they might do, is make a new series featuring Johnson. Before Mastercheif's time. Like in some of their books.
halo is over rated and not as fun as most ppl make it seem...definitely NOT!!!
I think you arnt seeing the big picture. Halo is an epic game to the gaming world and does deserve being highly rated because it is such a good game.
How ever for me. I don't want their to to be a 4th Halo simply because Halo 3 rounded up the ending of the game series pretty well. A 4th Halo would quite possibly kill the storyline. Not to mention it would be hard to keep it going because of the 3rd Halo being so awesome it would be hard to top it. xD
If the creators really wanna make a new game. Make a new series... Other than a 4th Halo.