Go look at the Anandtech individual game comparisons. They’re sad, and far from “10-15%”.
And if the throw down is games it can play that the 5870 can’t, my 3 yeard old 8800GTX could play almost every single game on the same resolution with tolerable framerates as both cards.
To answer your question, no I’m not disappointed. I was expecting it to perform equal to or less than the 5870 and cost $700. You were too. Why you’re so bent out of shape about it being a little bit faster for a little bit more money is puzzling. Maybe if Nvidia had the alternate cashflow of a CPU market and could bank on money from dozens of lawsuits against Intel in every major court on the planet they’d have released a card that was this much faster and then sold it below production cost, like ATI does.