I don't get the appeal of Soos.
I think he's just kinda bland and stupid.
100 Greatest Action Movies - http://www.imdb.com/list/ls000708268/
I think what I like the most about Soos is how he has developed a different relationship with each of the other characters.
I love the strong sibling-like bond that has developed between him and Dipper and Mabel. While with Wendy, it's more like a good friendship.
And he clearly loves Grunkle Stan and sees him as a father, which, I think, adds an interesting layer to the show. (Much better then if it was a simple employee/employer set up.) I just hope it can be repaired after "Not What He Seems."
He's developed a bit on the show. The writers could make him smarter than just the "dumb fat guy," though. That being said, he's one of my favorite characters. Soos is one of those TV characters who makes you crack up, even if he's in the background.
Weird is the new normal.