Halo is Crap? are you insane? I wonder why it breaks every record there is as far as sales go. Maybe because just about everyone wants to play it? If it were crap it wouldn't be the biggest selling game ever. Halo 2 was now Halo 3 is. If people thought halo 2 was crap, Halo 3 wouldn't have sold like it did and currently is.
If you have never played Marathon BACK in 1994/96, you will never understand...its mix of storyline, puzzles and action are unmatched, and Halo cannot compare to its intelligent design. And as far as "best-selling" software is concerned, you may use the same analogy for Windows...everybody has it, therefore it's wonderful...no thanks.