As used for apps on phones and tablets.
Pro Widely-used technology
One of the technologies that has the most developers. The documentation available dwarfs all other solutions.
Pro Open standard
Approved by the W3C.
Con Not a GUI Toolkit.
This is an off topic answer, that confuses the issue.
Con Slower than native
All HTML5 applications tend to be slower than their native counterparts.
Con Limited direct hardware access
OpenGL/OpenCL/Cuda/USB for example.