Get Boss Gallery:
Get 100% Logbook Scans in Art Gallery 4.
Unlock Character Gallery:
Get 60% of Logbook Scans in Art Gallery 2.
Unlock Creature Gallery:
Get 80% of Logbook Scans in Art Gallery 3.
Unlockable multiplayer extras:
Darkness Soundtrack: Beat game
Dark Echoes Soundtrack: Beat game
Luminoth Soundtrack: Talk to U-Mos
Pirate Fear Soundtrack: Talk to U-Mos after restoring power to Agon Temple
Torvus Bog Soundtrack: Talk to U-Mos after restoring power to Torvus Temple
Pipeline Arena: Talk to U-Mos after restoring power to Torvus Temple
Sanctuary Soundtrack: Talk to U-Mos after restoring power to Sanctuary Temple
Spires Arena: Talk to U-Mos after restoring power to Sanctuary Temple
Unlockable new endings:
Get 75% of items in the game, and you'll see Samus outside of her suit after beating the final boss. Get 100% of items, and see a special ending with Dark Samus.
Unlock promo gallery:
Get 40% of Logbook Scans.
Unlock Rough Sketch Gallery:
Beat the game on Normal Mode.
Unlock Samus Body Suit Cinema:
Get 75% of items.
Unlock Storyboard Gallery:
Beat game on Hard Mode.