Dang, I think I still want a Mario RPG that looks like that.
If the people who worked on Paper Mario read that...
I mean, I think Paper Mario was made with a team that new very very little about 3D. All of the geometry is rather rudimentary. Lots of vertices are disconnected for some reason, making little gaps in the world that can be seen when playing the game in HD. Some objects' UV maps are a little strange. None of the 3D animation is especially complex. All in all, nothing in the game looks like something I wouldn't know how to do by now, and all I've got is what I've taught myself by making Smash Bros. mods. But they got it to work, the 2D animation and the style used for the textures carry the game's visuals enough that it has aged much better than other N64 games.
But that beta screenshot... well, the fronds on the right side of the trees are backwards. If the grass has a texture, it sucks. Really weird things are going on with the foliage in the background. The dark L-shaped object in front of those boxes does not look enough like anything. There is just one cloud, that's no good for a background that blends into the background, it draws the eye to one spot. Same for the two berries. And remember what I said about PM's 2D animation carrying the game, making up for the 3D? Good luck accomplishing that with SMW sprites. This beta screenshot is like the sprite webcomic of video game art.