The Train Defense engine has now been upgraded from fixed pipeline to shaders and running happily on my ipad2 again at a lovely 60fps. I wasn't planning on having to do this, but its great to have the flexibility of shaders. I always found the fixed pipeline very restricting.
I've added a point sprite particle system for effects. I haven't tested what the maximum sprites is that I can push yet, but seems pretty good. On PC its crazy - I can fill the screen with 150,000 particles and not drop a frame. I expect iPad2 will be a fraction of that, but so far so good.
Now I'm putting in some start game camera sweeps and basic structure. Once I get some controls in for the train I should have the most basic prototype going and then I think it will be time for a youtube video.