Many viewers complained that the latest Game of Thrones episode was very dark - too dark infact to see what was happening during the Battle of Winterfell. The episode's Cinematographer says that the scene was dark intentionally, to make it extra intense, claustrophobic and disorienting. However he also blames the compression, and the display settings and viewing environment of most users.
Viewing the episode on an OLED TVs however makes for a good viewing experience with its high contrast and HDR settings. According to reports from the US, this has increased the interest in OLED TVs. Popular Mechanics, for example, ran an article titled "Games of Thrones Proves Why You Need an OLED TV" and Consumer Reports and CNET both recommended an OLED TV over an LCD for the specific episode.
Not really necessary an OLED tv... I have an old Sony 4K led 850C and I was able to watch the episode with clear images and no artifacts, partly by the player's configuration (Media Player Classic) and partly by the quality of the digital release (I use a "Memento" 1080p release with just over 5 GB, and it was very good).Then it is totally possible on an LCD tv.