The final release of SQL Server 2008 R2 was made publically available on April 21, 2010! SQL Server Express continues to ship in 4 different packages. In this release of Express, we simplified the installation wizard. For the November CTP release, I documented the Express installation process at http://blogs.msdn.com/petersad/archive/2009/11/13/how-to-install-sql-server-2008-r2-express-edition-november-ctp.aspx. The installation process has not changed since the November CTP, except some messages have been changed to indicate the final release.
I posted more information about this release to http://blogs.msdn.com/petersad/archive/2010/04/26/installing-sql-server-2008-r2-express.aspx.