I have subscribed to Netflix instant streaming for several years now, and I am generally quite pleased with their service & offerings. It does look like HBO & Showtime are missing from their offerings, and some TV programs are only partially available. Overall, however, their TV program collection is quite varied, and includes a number of older programs from the ‘70s & before that are difficult to impossible to find on cable.
Their movie collection is impressive and far flung. In terms of year of release, their movie collection spans more than a century, with 1913 as the earliest release date. At the same time they are collecting a surprisingly far flung collection of foreign movies as well, including fairly recent movies from South Korea (quite good, actually.)
Whether Netflix is for you or not really comes down to: what do you enjoy watching?
Then there is the other factor to consider: switching from cable to Netflix can save a LOT of money every month. (With my cable company, Netflix is about $62 a month less expensive than basic + basic digital cable.)