The guy who wrote DisneyWar was not really an independent third party, he was sanctioned by Eisner and was allowed to follow him around for quite some time gaining important insight on key situations. However, James Stewart also didn't have a very high opinion of Eisner during the whole ordeal...so to say that it isn't biased is just ignorant. (actually anyone who thinks you can get a complete understanding of something from reading just one book is ignorant as well). While it includes multiple perspectives, the author still uses those perspectives to make his point and tell the story.
Why would you not want to read Work in Progress anyway? If you want to form an opinion on the subject and get as much information as possible you need to read both sides. And Work In Progress is a great example and exemplar into Eisner's thought process. While it skirts around some key issues (but does encompass both Katzenburg's dismissal as well as Frank's death), it's a key into what Eisner thought was important, and what situations and facts he homed in on...and how he really didn't see a flaw in his leadership styles. ALL of that is important to fully understand the rise and fall of Eisner and his Disney Company.
I've spent a few years researching the Disney Company and the leadership styles of the company's past CEOs. If you want to get a better understanding for the company, there's no way I wouldn't recommend reading Work in Progress.