CG has always been and will always be a hack I think - debating the best CG is kind of like debating the 'most realistic miniature'. The more real elements you include (ie. real sunlight, real objects, photographed background plates) the less there is to offend your eye.
To me, the tools are getting so good (GI, HDRI lighting, MoCap) that 'seamless/not seamless' is soon going to be the only judging criteria. Of course along with visual aesthetic which will always occur in film whether you're using a physical camera or virtual.