No special effects work can fool me into thinking that it's the real deal. Like, whether Godzilla is suitmation or CGI or robotic animatronics or stop-motion, I'll never be fooled into thinking that it's really a real Godzilla that I'm seeing. Not just because I know that a real Godzilla could never exist, but because the special effects work can always be detected, analyzed, and comprehended just by looking at it.
But, some effects work does allow me to suspend my disbelief while I'm watching it. When I watch a Godzilla movie, I am absorbed by the movie. And when I see the suitmation Godzilla, I don't think "That's suitmation". I just think within the realm of the movie and think "That's Godzilla". Of course, afterwards, I don't think back like "That was Godzilla that I saw in the movie". I of course know and remember what special effects it really was. It's just that during the movie, in the course of watching it, I am able to suspend my disbelief for the time being and enjoy the movie and the special effects. This is how it is for GOOD suitmation, animatronics, and all good practical effects for any kind of movie.
However, CGI is not like that. With CGI, I am not able to suspend my disbelief. When I see a CGI character on the screen, I am not able to suspend my disbelief and be absorbed by the movie. Instead, I immediately think "That's a CGI character", and I'm always pulled out of the realm of the movie. No matter how good CGI is, this always happens. Although, some CGI can be so good that after being pulled out of the realm of the movie, I can re-enter the realm, suspend my disbelief, and enjoy the movie. This is uncommon and doesn't happen much. It only happens with the best CGI (Jurassic Park 1 & 2, Matrix Revolutions, Terminator 2). With most CGI, it's bad and damn difficult to suspend my disbelief for any period. And with some CGI (Hulk, Yonggary, Manda in GFW), it's 100% IMPOSSIBLE for me to suspend my disbelief at all.
The most convincing special effects in my opinion are robotic animatronics. That is to say, they are the easiest to suspend my disbelief with when they are good. Stan Winston shows the epitome of how good robotic animatronics can be in films like the Jurassic Park trilogy and Aliens. Suitmation I would say is next in place for how easy it is to suspend disbelief for me. The best suitmation occured back in the days of Eiji Tsuburaya in the early Showa Godzilla movies and now with the Gamera trilogy and the later Millennium Godzilla movies. As for CGI, it has to be among the best CGI ever for me to suspend my disbelief at all, even after detecting it as being computerized. And lastly, stop-motion effects. Stop-motion is the one effects work that I can NEVER suspend my disbelief for, no matter how good it is. With movies like King Kong, I admire it for it's classicness and achievement for it's time, not for the stop-motion effects that I cannot suspend my disbelief with even for a second.
