The pros (excellent power, ability to hit for a decent average, athletic, moves well as a catcher, has great hands) on Joseph totally outweigh the cons (his inability to handle good breaking pitches and inexperience).
Obviously, as he plays more and more, he'll knock that inexperience one out of the park, and with his intelligence (players and coaches claim he spends more time in the clubhouse than anyone else) he should be able to get a hang of those breaking balls too.
Joseph has played his way to Double A in only a season and a half, just a hair behind the pace that Matt Wieters set. He should be Bowie's starting catcher, and with no other real catching prospect in the system, and could easily have AAA Norfolk within his reach in 2010.
Finally, the one trait that should help Joseph the most is the one that almost anyone you ask about him is sure to bring up first. Joseph is a tremendous individual.
He spends tons of time helping out the community, and makes regular mission trips during the offseason, many of those to Latin America, where he honed his Spanish speaking skills, yet another way he has been able to improve his game, making him a better battery-mate for a number of his team's Spanish speaking pitchers.