There’s a few loose ideas for iPhone games that I’m toying with at the moment. Shiva does a nice job of physics (it has the ODE physics engine integrated) so some kind of a sandbox physics game could be nice. It all depends on the limitations of the iPhone of course – from what I’ve seen, there is a severe limit on the number of separate draw calls that can be made if you want a decent frame rate. The number of unique moving objects is apparently much more of a limit than the actual number of polygons in those objects.
‘Block Thrower’ – I have prototyped an idea where you swipe to throw wooden blocks into the scene, where they collide with other blocks. Pleasant enough, but not exactly a core game concept yet. Something along the lines of a 3D ‘crush the castle’ might work.
Some kind of turn-based squad-level combat game could work. There are a few games like this already available for the iPhone of course; but I have learned through Darkwind that this is a niche within the turn-based genre that is relatively popular. I would use the Darkwind critical hits table, one of the coolest things it has – seeing a textual description of injuries is so much better than being told ‘you hit your enemy for 5 damage’.
Back in the mid-1980s one of the games I wrote for the BBC Micro/Archimedes was called ‘Killer’ – a squad-level turn-based shooter where you could design the maps for your friends, define the routes that the computer-controlled enemies would take, and then level-up your characters and watch them die. We need perma-death, obviously. Killer was one of the most popular of my games amongst my friends.
People love to design things. Community can evolve from sharing maps, working together and participating in ‘player versus computer’ multiplayer combats. So this ‘Killer’ game would definitely need to have a scenario-designing component and some form of AI scripting component. Perhaps you could also script the AI defenders of your base if your base was attacked by other players.