Bad CGI: the Star Wars prequels are some of the worst CGI. it's very obvious because it's completely fantastical for the most part. And EVERYTHING is CGI except the human actors. It looks very flat. It has the effect of a 70's TV Sci-Fi show with the human actors clearly layered over artifial backgrounds. I think anything we're fictional places, creatures, people are portrayed in daylight situations the CGI has to be top draw otherwise it stands out like a sore thumb and looks like a computer game.
Good CGI: Used subtly things work a lot better. Real world locations that are already believable so blend in well. Your mind excepts them more readily. A great example is, another Ridley Scott film, Gladiator. Loads of CGI in that but it was for the most part quite subtle and blended very well. CGI also blends better and is more effective when shrouded in darkness or back light. Some decent examples of this on War of the Worlds. The back lit tripod that comes out of the ground in the middle of the day, with the sun behind, becomes a stark sillehoute. If the light sunlight was shining right on it (i.e. Behind the camera position shining towards the subject) suddenly you need a lot more detail and it's more obvious your looking at a CGI object.
The bottom lime for me is that subtle, stark CGI works a lot easier. Well lit, close to camera CGI looks like a dogs dinner unless it's absolutely amazing, believable, state of the art work. I think the new Planet of the Apes films have some of the best examples of this I've seen. Amazing lighting, texturing, motion capture. It's very impressive and I think will age well as a result. Most companies, if they tried this, would fall flat and the film would look crap as a result as the CGI would be obvious, which I think always detracts massively and is detrimental, if not totally destructive, to a movie overall. The Dog Alien on the ceiling in Alien 3 is an example. It looked like a reflective blob with mirrored appendages. Truly awful.
