For the price, the Oppo is one of the best players out there, thrilled that I bought one, and couldn't be happier - fast and plays tons and tons of different formats, very hard to beat.
My buddy has the PS3, and its a very good player, but he's still going to get a Oppo after messing with mine.
A few things:
Do you need playback of DVD-A or SACD? Oppo has both, Denon does not.
Do you need an RS-232 port? Standard on Denon, extra on Oppo
Do you need wireless ethernet? Oppo has an add-on, Denon is not capable.
You also want to consider load times, and customer support. Disc encoding is constantly being updated. Oppo has been ahead of the curve with their firmware updates. Other manufacturers tend to take their time in providing solutions to firmware issues.