Watching a Let's Play allows me to follow the story and evaluate the aesthetics better, see if they appeal to me. Saw Jacksepticeye's run of God of War 2018 and Unravel, All the Shinies' go at Prey, The Rad Brad's playthrough of Dead Space, for example. As a result, once I get my PS4 and a bit more entertainment budget, I'll likely be getting these games. (And redecorating my house in Neo Art Deco style because Prey is gorgeous even for a game about shooting brain-sucking slime monsters.)
Let's Players who aren't very good at gaming tend to make me crazy. Markiplier is adorable, but when he plays anything that isn't a menu-based indie game I find myself unable to even, and move on.