Used to describe things designed to astound in a wide-eyed youngster kind of way. Modern popular usage is for describing chrome, eye-candy, and creeping featuritis in a derogatory sense. On the other hand is the stereotypical 50's teenage boy (see Batman's sidekick Robin) who exclaims "gee-whiz!" upon seeing just about everything.
In my own manner of speaking I use 'gee-whiz' in a wistful, semi-satirical sense. In particular I do not use 'gee-whiz' when I feel the engineered astonishment is so great as to cheapen the thing but when I don't really see the point. So it's not that the developers are wasting my time, but only their own. A good example is a video game like Tribes 2 where the graphics have been updated without much improvement in gameplay -- it's not that the graphics bother me, it's just that I would have been happy without.
1: According to Merriam-Webster OnLine