There's still improvement to be had since even the best looking games of today don't hold a candle to high quality CGI seen in things like high budget films. That gap is a lot smaller than it used to be though and I expect that sometime within the next 15 years or so that true photorealism or close to that will be doable in real time graphics and eventually some time after that visuals on that level will become cheap and easy enough to produce for even small indie teams to have in their games. It's gonna be really exciting when that happens.