Single player

in Halo 1, 2, 3, 4 In this game you are a badass space hero launching bombs and guns upon moronic aliens and hungry parasites to stop some random space ring from turning you and your friends into dust

In Halo Reach you are a Noble space hero defending reach from the moronic aliens before the ship from halo 1 goes to the random ring of death

In Halo 3 ODST you are a weaker unsung space hero fighting for survival in an alien occupied city in Africa

Multiplayer
Blood Gultching chaos on over 100 quality battle fields from battle creek to Valhalla to Icebox all with vehicles and power weapons in 2 of the games you can fight a survival mode vs the AI on single player maps

this collection is worth £300 minimum but during a sale you get all 6 classics for a mere £7
also most of the games have dedicated mod tools NOW WITH STEAM WORKSHOP SUPPORT AND CUT CONTENT BEING RELEASED THROUGH IT and some of the games have a level editor called forge perfect for making your own multiplayer battle fields or lousy recruiting bases