I own the Oppo and auditioned the Denon 3800 when it first came out. My impressions of the Denon are not recent but here is my opinion based on my experiences with the two:
Pros for Denon: Build quality, slightly better sound quality via analog outs
Pros for Oppo: User interface, speed/responsiveness, frequent firmware updates improving player performance and compatibility, Oppo customer service
I would still buy the Oppo even with the price reduction on the Denon, which is happening because the 3800 is being closed out for newer models. The picture quality between the two is negligible (maybe slight edge to Oppo based on VRS processing). The Denon is extremely SLOW to respond, load and play a disc, etc. while the Oppo is the fastest player out there (basically tied with the PS3).
Hope that my feedback is of value to you - good luck with your decision.
P.S. I wanted to note that I no longer own a stock Oppo - I had my BDP-83 modified by Dan Wright and the quality of the analog output no longer even remotely resembles stock

I will post my review/impressions shortly...