Ross said in one of his blog post that he is looking for a new engine to make a machinima, and he listed what he wants and expects from the engine.
Well, did he consider trying Serious Engine 3.5? Or at least Serious Engine 2? It allows for good animations, lipsync, camera control, lightning, does not have many bugs, is easy to use (relatively) and all the tools are together in one program, Serious Editor. And it allows for HUGE maps and hundreds of enemies on screen. You get the Serious Editor by purchasing a Serious Sam game (e.g. SS2, or the SSHD remakes, or, the best, Serious Sam 3: BFE).
Here's a video demonstrating its capabilities:
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Hope I helped.
Cheers!