I think that Joe Johnston is a good director, I have seen recently Wolfman and I have really liked this movie, he have done imo a good job despite the big problem behind the production.
I think he will do a good job also because Marvel is behind him in the production, in comparaison, I think that Johnston is a better director that Letterier, before the incredible Hulk, Letterier don't have done great movie, just some action movies (Transporter, Danny the Dog) who was imo not very well done (and I'm a big fan of Jet Li), but he have done a fantastic job with Hulk, so with the Marvel production, I think Johnston will do a very good movie.