One of the biggest letdowns in Double Dragon III: The Sacred Stone NES is the lack of innovation. The game feels like a rehash of its predecessors, offering little in terms of fresh gameplay mechanics or exciting new features. The formulaic approach results in a repetitive and monotonous experience, especially for those familiar with the series.

Furthermore, the graphics and audio fail to impress. While it's important to consider the NES's limitations, other games of the time managed to deliver visually appealing and immersive experiences. The character sprites are bland and lack detail, and the environments feel uninspired and repetitive. The sound effects and music are forgettable, failing to create an engaging atmosphere.

Another major issue with Double Dragon III: The Sacred Stone NES is the unbalanced difficulty. The game starts off extremely challenging, with enemies relentlessly overwhelming the player. This high difficulty level might appeal to hardcore gamers seeking a tough challenge, but it alienates casual players who simply want an enjoyable experience. Moreover, the lack of a proper difficulty scaling makes the game frustratingly unfair.

Additionally, the game suffers from poor controls. The characters feel clunky and unresponsive, making it difficult to execute moves accurately. This lack of precision severely impacts the gameplay, leading to frustrating moments and unnecessary deaths.

On the positive side, Double Dragon III: The Sacred Stone NES does offer the option to play cooperatively with a friend, which can enhance the enjoyment to some extent. However, this feature alone isn't enough to redeem the overall flaws of the game.