The touch controls for sandstorm and NOVA really aren't that bad, they'd be perfect if the multi touch (or whatever programming the games use for multi touch) wasn't a little buggy. Sometimes I'll be going left and trying to shoot and what not and it will just do something completely different like move the joystick to a place between my two fingers... not sure why, seems to work better if i apply more force with my joystick thumb. If you turn off the aim helper thing i'm pretty sure it'd be damn near impossible at first, or if you turned the difficulty up, but honestly they could have done a LOT worse (like the quake 2 and 3 ports.)
If I had my choice though, I'd much rather use a zeemote in my left hand and the aim/shoot/grenade by touch, but that's just me. Chances of a developer supporting a third party accessory in addition to developing games for so many platforms (android, ipad, iphone, ipod, other smartphones) just doesn't seem likely.