Contrary to Mattevt's review, the character of Angela was not only none of those things described there, but indeed brought out the best of Shawn.
Now, unless one prefers a character to not go through any character development and stay the same way they were when they were 12 years old in the first season, I completely disagree that Shawn's character declined in any shape or form during the senior year of high school [where Angela is informally introduced as Topanga's friend and dated Shawn for 2 weeks]. Shawn finds a purse a girl lost at school, he falls in love with the contents of her belongings due to similar interests and intriguing materials, and is willing to date her. A confusion mix up ensues, when while the purse belonged to one girl [who already had a boyfriend] the things in the purse belonged to Angela, the girl he had just broken up with due to his 2 week rule of dating.
Based on the purse he finds, he learns that Angela listens to Vivaldi, enjoys Van Damme movies and reads William Shakespeare. Because of their shared interest, he officially asks her to be his girlfriend again when Cory sets them up on a date at a fancy restaurant (only to realize that they both prefer less formal conditions). After watching Topanga and Cory, who were also on a date, they decide that they both would like to have a relationship like theirs.
She was fun and outgoing, and a great best friend for Topanga -- far away from 'whiny' 'annoying' and a 'downer'.
Though the actress pales in comparison to the rest of the cast, she had immense chemistry with Rider Strong. Her comedic timing was fair, and her dramatic scenes were a hit or miss, but overall I would say she was decent.