World Size depends on a lot of things like: number of Triangles (10'000 to 500'000), Number of surfaces, Fog/NoFog/camerarange, VIS Occlusion?, Number of Animations and last but not least: your Definition of Hardware Requirements for your Release.
Some things are easier, some are trickier. One Goodie is you have to animate a Model only one Time and then you can display it from every possible angle, unlike in 2D.
To rotate a camera around an animated Mesh, say a bullettime-jumping KungFu Fighter takes you 2 Minutes of Coding, while it would be pretty impossible in 2D.
But to model and animate a decent KungFu Fighter might take you a day or two. Unless you gonna use Psionics "Ninja" ;)
Some things are easier, some are trickier. One Goodie is you have to animate a Model only one Time and then you can display it from every possible angle, unlike in 2D.
To rotate a camera around an animated Mesh, say a bullettime-jumping KungFu Fighter takes you 2 Minutes of Coding, while it would be pretty impossible in 2D.
But to model and animate a decent KungFu Fighter might take you a day or two. Unless you gonna use Psionics "Ninja" ;)