Character Design: Cheeky, quirky, funny, and cute. Poshul is a charming character.
Combat Usefulness: If you use her throughout the game, Poshul is much more of a tank and physical powerhouse than her image implies. Not as deadly of a pure attacker as someone like Karsh, but it's notable that Poshul on average has a higher hit-point rating than Serge and can do very notable damage on the physical side when trained. A lot of people are oblivious to this, since they shelf Poshul after the early stages of the game.
Tilt: Poshul doesn't have much of a backstory to speak of, but she doesn't need one. If you recruit her in the very beginning before you leave for home-world, she adds a lot of color and personality to an otherwise dreary section of the game, and it's also noteworthy that she is the only character that you can recruit before being teleported to Another World. Speaking of which, I've found that having her around after being teleported to Another can be rather comorting, because it feels like even though all the chaos of the game, you always have a little piece Home World with you in Poshul and all of her comedic goodness. XD Poshul is just a tongue-in-cheek character, and some people blast her for it, not realizing that she isn't supposed to play a serious and important role in the game - there are plenty of other characters to do that if you wish (though I generally don't like the generic, angsty "badass" characters that are all carbon copies of one another). Having Poshul in my party is always a delight.
Final Grade: B. Poshul is my favorite character in the game and as such SHOULD have gotten an A from me, but I'm trying to be objective here.