My PZ850 is still pretty dark years later. Couple things I'll share:
1. It took me a while to get used to the darker picture. After all, are things really supposed to be this dark!?!? Often times, the answer is yes.
2. To me at the end of the day, the video settings are a matter of personal preference. Yes, there are "optimal" and "calibrated" settings, but the fact is it has to be enjoyed by you, not the ISF or a tech standing in your living room critiquing your setup.
3. I noticed that my PZ850 varies in darkness depending on the source material. With certain satellite channels, it's not so dark. Certain movies and 360 games, I need to mess with the settings to see important details. The other day I was playing Deus Ex and I could not for the life of me see an object I had to interact with to end a quest. I had to crank up to max brightness in the game's settings to see it.
4. Every TV is different, so someone else's settings might not look good on yours. I used Avia II DVD to mess with mine. Do you have access to one and the filters? You might just need another tool for setting it up. You can also check AVSForum for people's settings, but again, they might not be ideal for yours.
Good luck. If I can be of any help, feel free to ask. I can provide my settings when I get home, on a biz trip right now.