There's a noticeable difference comparing texture quality, shaders, and subsurface scattering. Lastly Decima is one of the very few engines that have really good eye shaders. Just compare both gameplay models here. Uncharted 4 rarely even has subsurface scattering activated during gameplay while Horizon seems to have it turned on at all times. Important to note that these are both gameplay photo-mode models and not cutscene models that clearly do not represent what gameplay looks like (I'm not sure if Horizon features improved shaders and other effects like Uncharted 4 did).