I've got a few ideas.
-The obligatory Toa/Dark Hunter War idea. Something along the Transformers: War for Cybertron series, but in Metru Nui. For story/campaign mode, you'd get to play as Lhikan, Nidhiki, Naho, etc. and for multiplayer, you'd get to make your own custom Toa or Dark Hunter.
-A Soul Calibur-style fighter with Glatorian. You'd get every character from 2009, and possibly even the ability to make a custom one. If I remember correctly, didn't 2009 have some Glatorian fighter game? Still, this would be more along the lines of a traditional 3D fighter, over-the-top special moves, combos, cheesy pre-battle/winning quotes and all.
-An action-adventure game in the style of Star Wars: The Force Unleashed, covering the 2001-2003 story arc. Instead of Force powers, you collect masks and get mask powers. You start off with one Toa (I'm thinking either Kopaka just like in the comics, or Poster Boy Tahu), and unlock the rest as you complete stages, and can freely switch between them. The final boss battle would be Takanuva vs. Teridax. Maybe there could be a DLC storyline where you play as the Toa Mata before they crashed on Aqua Magna. Like, while they were still training and that one time when they went to Karda Nui.
-A game about Helryx's early quests and adventures starting with her creation as a Toa. I'm thinking something along the lines of Devil May Cry/Bayonetta.
-A Smash Bros-esque party fighter where just about every canister set character is playable. Or at least as many as they can fit. Not sure how they'd handle characters who have been released multiple times, though. You'd get items a la Smash Bros, like disk launchers (which work like the laser gun), a Zatth (summons a random Rahi, basically like the Pokeballs), among others. Whichever characters got Stars sets would get their Stars versions as unlockable alternate costumes.
Edited by Shinken Green, Jun 25 2014 - 11:35 PM.