It's because it's over-rated, not nessecarily bad, just over-rated. The story is not laid out well (i.e. series begins after a major part story which is in a god-awful book, Halo 2's ending) and neither are the charactors. Gameplay was dumbed down severely with shields and over-powered weapons that throw tactics out the window and off a cliff. Before you call me a Halo-hater, I love Halo. The first one being the FPS I ever played after BF2142 and being one of the nearest and dearest games to my heart. It's just that Halo dumbed stuff down and left out story elements. Really the series should have been laid out with the Halo Reach and Halo CE being the first, the 'First Strike' book (which I've never read but know is a tie in of H1 and H2) and the first half of Halo 2 with some stuff maybe added for Halo 2 and the last half of Halo 2 and Halo 3 for Halo 3. Also would've like to trade shields for cover system and acrobatic and strength based gameplay element because, let's face it, the games don't do justice to what a super soldier should be able to do.