Wow this is actually really faithful and the animations almost perfect. I saw another mod for 64 recently when the "PC version" came out and it was horrendous. They should redraw the UI though, rather than just upscale it.
The issue is I still think this doesn't ultimately work, you can't change the shading style to something more modern and keep the same basic models (Even if its many more polygons I know) because everything starts to look like Lego/plastic and it doesn't fit the aesthetic of the old game, which is kinda... dusty? I don't know how to describe it in words really. Its due to the rendering techniques/HW of course and not just artistic vision but I don't know if they would've made it look like this if they could've, maybe it would have looked like the modern 2D games with the "old titles manual/concept art" style graphics.
I'd still say play the OG game but if you have to have sharper/more modern graphics and higher perceived fps then I'd say this is pretty faithful work. Bowser does look like he's put on too much fake tan though lol