Don't get into webOS details as another article will cover that.
So more on hardware and here the cheap 55" UHD has to compete with the very good competion and does not completely live up to expactations.

* as in review for smaller LG lcds mentioned, the black level and local dimming is a problem
* also mentioned in reviews for other LG models: gaming lag is too high
* 3D also has issues

LG 55UB950V Review | TV Reviews