I can't speak to the L83 G20 driver, but compared to the lesser G20, the Rocketballz driver was surprisingly good.
I agree with YJ about the trajectory of a full set being an important factor, but I think it's less important with drivers.
I fount the RBZ driver to be much longer (10 yds +) than the lower level G20 without sacrificing any playability i.e. you can maximize the drive by appropriate use of backspin, etc.
Comparatively, I would put the RBZ driver on a par with the R9 Super-tri, with a much easier to ding meter speed.
I expect the upper level G20 to be 5-10 yds longer than the RBZ, but that's just conjecture.
The downside to the RBZ driver would be diminished accuracy. If you're trying to drive the green on SA 9 or 10, or the 300 yard par 3 at Oakmont, you might wish for that extra dot of precision, but on the whole, the RBZ driver is a bargain for lower level players who want a big stick.
I'm sure the RBZ irons are probably crappy, and this review of the driver shouldn't be extended to include the rest of the set, but for a long hitting driver, the RBZ is a good value.