I've honestly never found any enjoyement watching Let's Play videos, outside of seeing the first minutes of a game that hasn't released in order to get me hyped. (But a full walkthrough?! C'mon!).
I love speedruns, because the dude playing has to challenge himself into knowing every single secret the game can behold, and exploit it into his advantage. Watching a video of a dude beating Dark Souls 2 under 25 minutes is fun. Watching a Let's Play of about thirty hours of a dude dying over and over and being completely clueless is not.