My biggest gripe with stuntcasting, at least currently, is the inclination to cast big name actors and stiff well-known voice actors. Don't get me wrong- bigger name stars often are great in the role- lots of Pixar movies, for example. But you can't tell me that in ALL of Hollywood- known and unknown actors- that Chris Pratt was the best voice for Mario. And I'd say the same for Charlie Day and Anya Taylor-Joy, both of whom I have no gripe with- certainly not to the extent of Crisp Rat. Even Jack Black to an extent- like, I get what they were going for, and it certainly does work, but I'd love to see a slightly more serious take on Bowser too.
Fan-casting is a mixed bag for me. Sometimes they're right on the money and the actor is perfect. A lot of times, they're not, but the fans just cast who they like in the thing, or whoever is most attractive. Sometimes the fan-requested actor doesn't get chosen, and it almost feels like there's a concentrated effort against the film, even if the chosen actor is fantastic in the role.
The one I always go back to is Heath Ledger. I know at this point it's been talked about ad nauseum, but honestly, who among us, even fans of his, were expecting that he had that in him? Or most recently Jacob Elordi in Frankenstein- another traditionally pretty boy (ironically also Australian) who delivered a very nuanced, heartfelt performance. I truly try not to judge casting until I see the thing.