I am the first to admit that I have literally no knowledge of video editing or production and if I were to try and create some form of game commentary video be it a let's play or a more edited type of video it would be terrible. But looking objectively as a viewer it is clear that a lot of the amateur gaming commentaries on YouTube are seriously lacking in...something. What that is can depend on the creator of the video or even the situation that the video was produced in. So what separates these content produces from the huge juggernauts of gaming channels that exist?
I feel that it normally comes down to situation and timing rather than actually quality of the video by this I mean that if you release a video just before a huge surge in popularity for a game it can boost a channel to huge levels overnight a perfect example of this is the shear amount of channels that exploded during Minecraft's rise to earning its inevitable place in the history books (do people still use those?). Northernlion is another example of a channel that gained popularity because of a specific game this game being his completion of super meat boy.
You will see that many of the unsuccessful channels release videos of older games simply because of their popularity but miss out on the initial boost that they could get around release. But this wont completely doom them many Call of Duty commentators have risen in the middle of its life cycle, but the main difference between these videos and ones with less views is that the ones with fewer views tend to focus on commentating on their game play while more successful producers tend to only briefly mention their game play and instead talk about other subjects to help appeal to a much wider audience.
First go at writing anything really, done on a whim, far too late at night, but worth a shot right?