yes it's worth it if you plan on using it (lol who would have thought)
i only got a 7 day one because most of the other traveling i did was with the gf's parents by car, so it wasn't needed. i got the ordinary class and didn't really see a need for a green class one
ordinary class on shinkansen is quite nice, way better than economy on an airplane.
i loved that week of having it, you don't have to wait in line for regular trains and don't have to pay for anything.
i used it all over with local/express trains and the shinkansen from tokyo eki to kyoto and back
so i think it depends on where you are going and if you really plan on using it, i surely got my moneys worth with mine and loved the convenience of it.