65" ES8000 Darkness Issue

The issue you are running into is called auto CE dimming. This can tend to crush blacks on properly calibrated sets. There is a workaround posted in the main UNXXES8000 thread, which I admit is a bear to get through.

See this post:

http://www.avsforum.com/t/1399319/official-samsung-unxxes8000-owners-thread/3480#post_22385782

Scroll down to the counteract CE dimming settings. Basically, you tweak the white balance sub menu then bump up the brightness to compensate, which tricks the set into no longer auto dimming

edit: Also make sure you have dynamic contrast set to off, as this will crush blacks.

It is confusing. There are two separate "features."

CE Dimming: You cannot disable this feature in any setting. This is when the set automatically turns down the brightness during dark scenes to minimize flashlighting and clouding that some sets have. You can bypass it as above

Microdimming plus: This is a misnomer that actually has nothing to do with dimming the set. It does some "active scanning" voodoo to tweak the contrast but does not do any actual hardware dimming. Most of us think it is fake and not a real impact on picture. It is on by default in all modes but movie mode, which it is inactive.

See this post: http://www.avsforum.com/t/1399319/official-samsung-unxxes8000-owners-thread/7620#post_22681768

Micro Dimming
"By maximizing the contrast between lights and darks, Samsung's Micro Dimming technology displays a picture that is as true-to-life as possible. Our innovative technology scans zones across the image and adjusts brightness to deliver deeper dark tones and brighter whites. It also eliminates the "halo" effect and image distortion that can happen with diffused lights. The Ultimate version of this technology optimizes the quality to new heights by scanning 2x the number of zones in the image. The result is a crystal-clear picture with realistic, vivid detail and accurate color reproduction."
http://www.samsung.com/us/video/tvs/UN55ES8000FXZA-features
"Ever watch a movie and find it’s hard to see an object in the background? Micro Dimming Ultimate analyzes each frame of video in hundreds of areas to optimize the LED backlight and video signal for each frame in real time. By increasing brightness in the areas of the frame that are too dark to see, an overall 20% increase in brightness is achieved and finally you can make out that zombie lurking in the dark! Along with an overall brighter picture, Micro Dimming Ultimate will also produce more vibrant and richer colors."
http://www.samsung.com/ca/consumer/tv-video/tv/led/UN55ES8000FXZC-features
Supposedly Micro Dimming Ultimate in the 8000s has 600 zones, which is double the zones that Micro Dimming Pro has in the 7500s. This feature is on by default in all modes except Movie mode. You can't turn it on in Movie mode.

CE Dimming
There is very little information on this technology, but here's what it does. During a dark scene, the panel will automatically dim itself to give you deeper blacks and less apparent clouding. The reason we refer to it as CE Dimming is because it is in the service menu named that way. There were past TVs that you could turn it on or off from the service menu, but you can't on the ES TVs. It is on by default on all modes except Movie mode and the profession calibrator's modes, Cal-Day and Cal-Night. Some people don't mind or notice it, while it drives other people crazy. It appears that it may be more obvious on the ES7500 series than on the ES8000 series though this isn't confirmed. Because of this, some of us think that it is somehow tied to the Micro Dimming zones. You will most likely notice it during credits in a movie, or perhaps a movie with a lot of star fields. It is also very evident in the very dark movies of the Harry Potter series, but hard to tell because the whole movie is darker. What you'll realize is that you have to bump your backlight up more to see the film correctly. Why? Because the whole film has been dimmed. The reason it drives some crazy is because of the following. Say you watch a lot of science fiction. The scene cuts to a star field and you see the stars dim over a couple of seconds. Then a ship or planet comes into view and you then see the screen brighten. It can be distracting. There is a way to diminish or possibly even disable this "feature" though. It reacts to a threshold set by the Brightness setting. The higher you have Brightness, the less CE Dimming comes into effect. The problem is that your panel is now hazy and not calibrated with a higher Brightness setting. This can then be offset by turning down each of the White Balance Offsets, R, G & B accordingly. If you turn Brightness up by 7 points, turn down each White Balance Offset by 7 points.

My ES8000 is plenty bright in dark scenes, most of my efforts in calibrating mine is to get blacks a tad darker !! Have you reset your picture settings to make sure some of the junk settings are turned off ? The first place to start is to make sure both your Bluray player and panel have their HDMI Black Level settings set to NORMAL. I'd also turn off things like dynamic contrast.