I know what TV_Themes says should be taken with salt, but there is a danger of movies that put graphics over storyline. A CG Bowser would at least be closer in looks than what we got. But then the whole movie would have to be done like that. Iggy would have to look like Iggy, we'd need an actual Big Bertha because... uh... I think they were underwater once, that's where Bertha can be... make the Goombas actual Goombas... and... no, actually, I don't know what a dark gritty Mario movie would be like. The happy-go-lucky vision we see contrasts too much with it. Maybe the original movie was on the right track. But the least they could have done is leave out names like Goomba and Big Bertha if they were going to be applied to humans. Bowser could use more CG and get away with it. But Goombas aren't meant to be six/seven feet tall, period.
Or, you know, just make a feature-length version of the Super Mario Bros. Super Show. It won't make sense, but it will look and act more like Mario.