Scrappy's only crime is being a sixth wheel... and that terrible cartoon series where Scooby and Shaggy are constantly chasing after him while running from some big guy he ticked off. Scrappy's actually quite good in 13 Ghosts. And not just because Flim Flam is more annoying. They just had better writers who actually knew what to do with the character. Better writers indeed, as they'd go on to work on a certain cartoon so beloved to the point where it would almost be considered overrated if you could find anyone who'd admit it... Narf.
Jar Jar was handled terribly. He's essentially Disney's Goofy with an annoying voice. He supposedly redeems himself in the Clone Wars cartoon. Then there's the whole thing about Lucas being open to collaboration, compromise (with others on the projects and reality when it came to special effects) and constructive criticism during the film making process of the original trilogy vs being surrounded by Yes Men and having his say in every aspect. I'm sure if someone stepped in and helped him develop Jar Jar, we'd like him a lot more.
As for the actual subject of the thread, about talking dog movies... there's something I dislike about their look. The obvious CGI mouths look terrible. And the only alternative is kinda worse. For the lack of a better example, Smurfs 2 featured a photo-realistic CGI cat with extremely unnerving cartoonish movements as Azrael. So the only other alternative is a creepy completely CGI version of an animal. Not stylized like Scooby-Doo, Garfield, and Yogi Bear (though they look pretty bad in their own right), an actual animal done in CGI, photo-reallistically. Personally, I liked the internalized dialogue like in Homeward Bound... but that somehow doesn't work well either. In live action, anyway. Garfield pulled it off.