Our 3 year old boy absolutely loves this show, and it's been a bonding experience with his older brothers (4 and 6). Like the show, they have simple adventures, use teamwork to try to get those pirates, and collect coins. There's an occasional positive message in the show, but I have yet to hear those messages referred to in their play... so I wouldn't give much credit to the show for character-building. At least it's not violent or laughing at drug use or whatever.
There are some downsides. For one, pirates are basically professional thieves... I don't know why they should be "fun". We've beat the message about real pirates into our kids' heads, so hopefully it outweighs the show. Second, only 1 of the 7 main characters is a girl, and she's clearly an accessory character. Just like most movies and shows in our culture, the girls barely exist, and if they do they don't lead anybody or talk much. Parents of girls beware.