Ronster said:

But as soon as you start to try to synthesize biological things animals / monsters / natural environments i.e. trees it falls over.

It just all goes wrong when it comes to trying to create something that is alive because we can feel that it is dead there is no soul or energy transferred by cgi.

But it does do dead things like real dead things

You are correct, the motion is actually far more important than the actual visual representation of the object. However, in case of CGI humanoid creatures, this problem can be solved easily. You just fit the human joints with marker and use real-time motion capture system to obtain the natural motion for CGI model. Dynamics matching will be pretty muach perfect.

On the other hand, this problem is very evident in practical miniature models where they try to produce a feasible motion. It is okay if you have a model of a massive space ship moving through space since the dynamics is really simple. But for example AT-AT motion and interaction with environment looks quite fake to me because the dynamics of the model is completely different from the dynamics of the thing that it tries to model.