Anyway I was trying to get some experiment to work and so far I try dynamic shadows, which is more fitted for outdoor game and guess what. this was terrible. Setting the shadow with the tree wasn't the hard task I was trying to push the system a little bit more but nothing really evolve. I think the reason most people use baked shadow is because it's was more stable than dynamics's. Unfortunately for me and people willing to do an outdoor based game we need more effort to get a decent result.
this is my first attempt to get something close to the result I got in Cryengine2
So yeah this is quite far from the realistic environment I had in mind but I have a lot to learn.