OpenSCAD, as noted by the author of the website sorely lacks a number fundamental features.

    - proper fillets

    - proper chamfers

    - surface-surface intersection

It is also limiting because it can only generate triangle meshes and can indeed be slow when models get big

However, for many situations, especially for prototyping, it is good enough and a really great tool.

It is definitely the first tool I turn to when I want to model a simple part quickly.