This is something I'm glad about - the R2 numbering system just confuses people.
Following is list of key capabilities that have been added to BizTalk Server 2010.
One interesting result of the renaming is that the lifecycle clock resets. For BizTalk 2009 R2, the 5 and 10 year support bands would have started with the release of BizTalk Server 2009 "R1" so you would effectively lose a year. For BizTalk 2010, the support bands start from its release ... some time in 2010.