Transitioning from the 2D style to the current 3D world can be hard, but these franchises were able to pull it off well ...

These Sonic games provide a nice balance between high-speed 3D gameplay and nostalgic 2D stages.

Despite the odd snag, The Plucky Squire makes for a fascinating interplay of 2D and 3D puzzles, battles, and diverse minigames that make it a paragon of the genre.

The game's visual style is a real treat: the majority of the action is isometric, but there are perspective shifts and camera tricks that see the world shift between 2D and 3D.

How a new emulator generates 3D scenes from 2D NES games The shape detection algorithms behind the intriguing 3DNES project.