i'd like something like Ace Combat, because the AppStore has almost no good story-driven flying games.
Portal would be great, but part of the whole Portal experience is Glados and i doubt Gameloft could pull off anything similiar without looking stupid. I don't know if it's been mentioned yet but a Ratchet and Clank clone would be cool IMO.
Turn based strategy. Either along the Civilization / 4X style of things, or something more like a SRPG like Final Fantasy Tactics.
Ditto. I would love to see a pokemon game for the idevices. Lets get to work on this man. I'll do level design and art crap. lol.
Gameloft Future Love them or hate them, let's face it: Gameloft is everywhere. They specialize in making console favorites into iOS games. So what should they clone next?
Yu-Gi-Oh/Magic Bullet hell Something with big robots in them (Gundam, Transformers and Metal Gear to name a few)
A Metroid knock-off would be interesting. Preferably Prime-type but the 2D type would be good too. (Well there is Grokion already.)
So, when's that arena fighter (aka SSB Brawl clone) coming to the iOS? I really can't think of anything that would be as much win as that if it includes multiplayer.