I <3 Halo:Reach - amazingly fun and best campaign + amazing Soundtrack
I <3 Halo 3:ODST - best soundtrack + Firefight + Coastal Highway and Mombassa Streets, amazingly unique campaign.
I <3 Halo 3 - best multiplayer levels + Forge + best Custom Games + soundtrack
I <3 Halo 2 - amazing huge fun campaign + soundtrack + Fun multiplayer
I <3 Halo: CE - started it all
4 billion points.
4,000,000,000 divided by 1600
=
2,500,000
2,500,000 times $20
=
$50,000,000 for a Map pack.