The change of halo is very big starting from the halo before halo combat evolved I think it was supposed to be for the mac operating system. But anyways it wasn't released to the public to use.Then came the halo combat evolved that got rated high and got awards for a awesome sci-fi first person shooter.It didn't have the best graphics but the storyline really made sense.Then halo 2 and this time the storyline I really didn't get but the multiplayer was great.And the difference was that you could hold a SMG what they didn't have in halo CO.Then came halo 3 thsi time your only enemy's those monkeys on steroids and the grunts that are really easy to kill.But for me the game was too fast and I managed to beat the game in one day on my spare time.Then came halo reach the best halo in the series with forge that for me was really fun.Then the multiplayer was cool too,the campaign was kinda boring in the first half of it but in the beginning and the end was fun I think that's pretty muck all the halos...bye