There are a huge number of fixes as well as some security related ones. Hence, it is highly recommended that you upgrade your installation. Mark’s got quick list of changes in 2.0.5 if you want to review in short what has changed.
I’ll try and see if I can churn up a list of modified files between 2.0.4 and 2.0.5.
Until then you may want to upgrade your installation.
Update: It has been reported that some users are facing a “Server 500 error” after upgrading. If you face this problem, you will need to install the WordPress 2.0.5 Tuneup plugin.
I believe this will be fixed in the next version.