Hands-down, it's Metroid Prime. Of the last decade, they go like this:
Metroid Prime
Metroid Prime 3
Metroid Zero Mission
Metroid Prime 2
Metroid Prime Pinball (yuk yuk)
Metroid Fusion
Metroid Other M
Hunters isn't included as it's the only one I don't own for some reason.
Let it sink in kiddies, after a while, you'll see why Other M is such a travesty.