I don't know anything about mastercam, but I've been using FreeCAD for several years now.
FreeCAD is full-featured in that it will do anything any other CAD/CAM software will do. However, it (like all CAD/CAM software) has a rather large learning curve to it and in many aspects it operates differently than other parametric CAD/CAM software.
Whether or not it's a viable alternative to other packages is hard to answer. It depends on what you value in those other packages. Technically speaking, FreeCAD will do what other packages will do. The only question is whether you're willing or able to devote the time to become proficient with it.
Disclaimer: I haven't tried out the new FreeCAD version yet, so some of the learning curve may be reduced. I don't know. Looking at the changes being reported, it does sound like they've smoothed over some of the rough edges to it.
