I've not eaten upstairs but have eaten downstairs.
You need to like that Spago-style California cuisine to like Wolfgang Puck's. If you do, you'll love it. If you don't, you won't. It's basically just american (and particularly californian) ingredients with french preparations, although that oversimplifies it a little.
Heavy sauces, odd combinations, and very nontraditional presentations is what it's all about. Horseradish apricot sauces, etc.
Ask yourself this -- what do you think of wasabi mashed potatoes? If your response is, why would anyone do that to mashed potatoes, then Puck is probably not for you. If, on the other hand, you hear "Salmon" and "Gorgonzola," and you think, "that might work," they you'll probably love WP's cafe.