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
Save it until you want something from amazon.
i've done the same stuff where i'd get an amazon giftcard, and I'd spend it within a day on something I really didnt need, then a few weeks or months later Ill want something really bad, but alas, I have no money on Amazon and wont be able to buy it.