In a recent discussion on Orihime Inoue, I mentioned that her design didn't support the powers she had, I also singled out the early Hinata Hyuuga as being out of place in a Shonen series.
While good writing can save a character it can ruin it just as well, ask Sakura why no one cared when she was left behind by Naruto and Sasuke.
There are ways to avoid problems later on by just getting it right first time and even on their bad days you still support them, so I'm going to tell you how to identify a good character by just a simple character picture.

With every character ever designed there is a default look to them that offers an insight into what type of character you can expect from them, a first impression is only 7 seconds so a good character design can give you everything in that time.
Using the strawhats above as an example, each expression, each pose is carefully selected with every piece of promotional art to make sure you know everything about these ten characters before you even open the book.
This is especially easy with male characters as their character traits are easy to read from a simple pose, female characters are more difficult to read as there is a good percentage of female characters that give off the same trait "there's a full length mirror in front of them and they are checking themselves out"
This isn't as bad as it used to be but it's still noticeable the higher up the sexy spectrum the show is.
Once you cross that bridge, the next one is compatibility with the world and it's universal laws, the question being, do you see any of these characters being in anything other than One Piece?
This usually makes or breaks an anime character, too many 12 episode series have this weekness where you feel that the character would turn up in a better anime or you see a different character instead.
Afterwards it really boils down to the plot to see if you still care about the anime once you see these characters in action. I've got four characters to bring up over this week to showcase some of these points.