The MS Word grammar checker only has three styles of grammar checks: Business, Strict and Casual. However, it gives reasonable explanations of grammatical rules, and furthermore, the user can determine if a document is "understandable" by examining the reading-level of the document. MS Word gives several readability statistics for a document which the user can use to determine the reading level of the document.
The WP grammar checker also provides good explanations for grammar mistakes. In addition, it has many styles of grammar checks, including Very Strict, Quick Check, Technical/Scientific and Fiction.
One rather humourous feature of the WP grammar checker was revealed through testing. This grammar tool warns the user if offensive words or profanity is used in the document. Much of our testing was performed by typing a document in both WP and MS Word, and noting the differences. By chance, one of the test documents was part of a Guantlet article about the musician Tori Amos. The article detailed some of the lyrics of her songs. One lyric was: "he likes killing you after you're dead/you think I'm a queer...". The WP grammar checker warned the user that "Using queer for a homosexual is considered offensive". The grammar checker also advised the user to consider changing a word when profanity was encountered.