Just to weigh in with a biased alternative to the engines...
We just put out a new product which is a bit lower-level than a game engine. It's called BatteryTech and it's a lightweight SDK that provides all of the Windows, iPhone, Android and Mac platform-abstraction services as the engines, but without requiring you to use an engine. We develop custom engines (it's not that hard, really) for our games and figure others want to as well, so take a look if it seems like what you want.