I know this was not to be taken seriously at all and was supposed to be all in good fun, but...yeah, I did cringe at times.
I watched the old Scooby Doo cartoon show as a kid, around 5-7 years old or so and I enjoyed it, so I went into this a little nostalgia-minded. I also remember Dean's comment back in S2 (Playthings?) about maybe running into the Scooby gang and "mmm, Daphne, love her." So I expected him to have a thing for her, but IMO that was one of the things they went a little over the top with. His disdain for Fred was good for a little chuckle though. Velma's crush on Sam was also kind of funny though a bit cliched. I did like the montage of them all running around to the Scooby Doo theme song.
It was kind of an interesting twist that this cartoon world was actually dealing with a real spirit and not some guy in a mask like they always dealt with, and that the Scooby gang was tough to come to terms with that. The spirit of the little boy talking about "the bad man" making him do these things sounds a lot like something that was done already in an SPN episode (don't ask me which one, I just remember seeing it before).
The part before they (Sam, Dean and Cas) left and were saying goodbye, Cas tells Shaggy and Scooby that he admires them bringing laughter in the face of danger...huh?? Was that just a throwaway comment played up for laughs?
Finally, the end where they get the "bad man" arrested... Dean is wearing an ascot. He hints he'll score some chicks with that now, I guess? Bad guy says the "I would've gotten away with it if it weren't for those meddling kids" line that was always said in the cartoon. Dean is orgasmic over this and he then says, ala Scooby, "Scooby Dooby Dooooo!" Um...lol, I almost felt embarrassed for Jensen there. ;)
Again, I know this was all in good fun and maybe I'll change my mind upon watching it again...and the very idea was cute, but some of he execution I just found a bit too over the top for my liking.