It depends on what your level of experience is, as well as what your goals are. If you are looking to stay in shape, then maybe a bowflex will do the job, but if you want to get big, you HAVE to use free wieghts (and some pulley machines).
IMO a better choice for a basic home gym would be a sturdy adjustable bench, a set of power blocks, a barbell, 200-300lbs of plates. Even with a basic set up like this you could put together a very good bodybuilding program...and you wouldn't really need a spotter.