The Metroid series is so littered with prequels and sequels that it's hard to tell where exactly Metroid II: Return of Samus sits in the story. It definitely takes place after the original Metroid, if that helps. The adventure sees the intergalactic bounty hunter head to the Metroid home world, SR388; her only mission to eradicate every last one of those energy-sapping creatures. The GameBoy classic is out today on the 3DS eShop.
Also up for grabs on both the eShop and DSiWare is the tower defense(ish) titleCome On! Heroes, while WiiWare gets the fishing title Big Bass Arcade.