The realism of the dinosaurs in the first Jurassic Park isn't just down to the CG, it's also the great practical effects (the T-Rex head is the greatest thing ever) and Spielberg's amazing directing. Spielberg made sure they didn't go beyond their capabilities. Imagine if in 1993 Jurassic Park they'd tried to do what Peter Jackson did in 2005 King Kong - a huge fight scene between Kong and three T-Rexes. The effects would have looked really BAD then. Spielberg was very subtle with the CG and so it worked really well.
No matter what, CG looks fake. Relying on it too much makes a movie lose a certain edge. I think King Kong JUST gets away with it because there are so many practical effects elements (the model work for Skull Island), and Peter Jackson wanted it to have a studio special effects feel. Also, Kong, like with Gollum, relies a heck of a lot on an Andy Serkis's performance. He's not just a CG creature. That helps a lot.