Very useful, if you use the Matrix in your games. Excellent for Technomancers.
Lots of programs and program options, and the Technomancer section is kinda like Street Magic; alternate traditions, Submersion Ordeals and additional Echoes.
It also talks more about weird Matrix phenomena, though, again, much has to do with Technomancers and Resonance.
There's not too many things for non-hackers.
Bottom line, must have if you use the Matrix in your games, not very useful if you don't.