They're worse or equal to boxed copies.
From what I've seen, basically, you can buy games one or two years after they're released, if they're popular they cost 30 euros (/Dollars, I'm assuming), if they're not they cost 20. The prices never go down. There are some sales sometimes, but that's only available for gold members. (I'm not one) There's never anything as crazy as Steam either.
They released Mass Effect 2 on the PS store at the same time as the release, and it was kind of a success. More than 10% of the sales were downloads, and the price was the same (60 dollars) so the profits were MUCH bigger per unit for Sony and Bioware. Hopefully they'll learn from this (and actually lower the prices some more... But I'm being optimistic. At least prices maybe wouldn't raise even with inflation)
Total ripoff compared to Steam obviously.