The best part of Gmsh is that it's open-source. Meshers are generally expensive and complex so the open-sourceness is its main advantage. Secondly, despite being open source, it's pretty powerful! It allows you to make structured and unstructured meshes and import complex geometries from other software. Review collected by and hosted on G2.com.

Most of the complex options aren't available through the GUI, so scripting is required. Also, the GUI sometimes messes up with the backend script, so the scripting part is pretty much mandatory. Finally, the scripting is not intuitive at all, and the documentation is weak. Review collected by and hosted on G2.com.