I was in Watch City (at Del Amo Mall in Torrance, CA) today and I held both the old G-Shock G3000 and its newer incarnation, the G4000.
I have to say I was underwhelmed by both. The differences are minor. One has a 9 numeral at the exclusion of the 3 wile the other has the 3 at the exclusion of the 9.
One thing to point out: Case size is listed at 50mm, but this is deceiving. You'd have to count the outer bulges on the left and right of the bezel. In reality, this dial looks like a 45mm, very small.
Since Amazon is selling the G3000 for $120 cheaper than the G4000, it's the more compelling buy.