doubleofive said:
This is 1 2 3 and 4, with upgraded graphics (flippable like Halo 1 AE), all the multiplayer maps, and if I read it right, switchable physics engines in multiplayer.
In Halo 1 and Halo 2 you can switch in-between the new graphics and the original on the fly while you're playing. Each game gets it's original multiplayer running on the original game engines.