It appears Rai is asking about the function of a designer on the grand scheme of game production. As I understand it, the designer creates the layout of the playfield and objects for the shots, so the full actual design of the playfield and shot layout was made by joe balcer. His other games in my very opinionated opinion are total duds. But it is believed that since everything is on the line, this will be better than his finest game, which of course is Simpsons presently.
Doing the programming and here on the boards is arguably the best software/rules programmer of all time. Many argue that Lyman at Stern does better programming, but that's also a debatable issue. Johnson seems to have the most depth in rules in that there will be details in games such as Lord of the rings and simpsons, that people could play their whole lives and never see the wizard modes. Again, everything's on the line, so no slouching there.
Buying the game is a risk, buying any game is a risk. Even buying the next Mario is a risk, remember Mario Sunshine? Me neither. Not everything is a home run in life, but a lot of factors have been brought in to make sure that this game isn't a dud, so people are willing to take this risk. Of course, this isn't being exactly bought sight unseen either, images and information have been trickled out, and the game will still be buyable after release, just maybe not the LE's at that point.