I got the OPPO DV-981HD model last month for my Samsung HLS-5687W and I saw very bad macroblocking enhance issue with it, a little worse than the macroblocking I also saw when using my Denon 1920.
Although DLPs and plasmas are vulnerable to macroblocking, it really depends on the quality of the DVD. On most DVDs, the macroblocking either does not exist or was barely noticeable under specific conditions. But on some DVDs specially those with a lot of dark and interior scenes, the macroblocking was very distracting and annoying. It shows up mostly on the background of interior scenes like walls or doors.
I had the display ISF calibrated and the macroblocking was diminished by only a fraction. The macroblocking is even worse when using players based on the Genesis Faroudja FLI-23XX series deinterlacers that most Denons and Oppos 971 and 981 use.
I originally bought the 981 because it upconverted to 1080p unlike the 970 which can only go to 1080i, but finally, I could no longer take the Russian roulette that I was playing when watching DVDs, where I would be praying that the next DVD I would watch would not be one of those few that showed macroblocking.
So I exchanged my Oppo 981 for a 970 and wow, what a difference! The macroblocking has totally disappeared. I am so happy with my 970! The picture quality is the best I have seen in a DVD player under $850 and any other player worth more than that would only have a little better picture quality. You would have to go to HD-DVD or BlueRay for a significant improvement.
Putting the macroblocking issue aside, I saw no difference in picture quality between the 981 upconverting to 1080p and the 970 upconverting to 1080i and both seemed to have a little better picture and audio quality when compared to the Denon 1920.
All things being equal, the picture quality of the Denon was a little better through component when compared against itself through HDMI. While the picture quality of the 970 was better through HDMI when compared against itself through component. The picture quality of the Oppo 970 was the same through component as the picture quality of the Denon through HDMI.
And both Oppos and the Denon were better than my Xbox 360 or its HD-DVD player for upconverting DVDs.
I had considered buying the Denon 2930CI instead of the OPPO DV-970HD because the Denon does not use the Faroudja chip but the $700 difference did not justify the little benefit in picture quality. Better for that money to go for a video scaler.
The Oppo 981 is a great player that should be selling in the neighborhood of $800 instead of $230 but if your display is vulnerable to macroblocking, I would suggest the Oppo 970 instead which should be selling in the neighborhood of $750 instead of $150.
Just my 2 cents.