I listened to an Entity Framework podcast from Channel9's "Expert to Expert". Brian Beckman (a mathematician at MS) interviewed Sam Druker (GM of the Data Programmability group) about the design and philosophy of EF.
It was a very interesting discussion and helped to position EF in comparison to the other O/R options out there. There were a couple key points that stood out to me:
EF is not just an Object / Relational mapper in the classic sense of the word. It's scope is much more than just translating a .NET class into a SQL row.
They think of EF as a superset of SQL's relational theory, which is based around sets, relations, rows and tables. EF understands these theories and stays true to them. EF goes further and addresses additional concepts like inheritance and associations.
I cannot explain it nearly as good as they did, so watch the podcast. (http://channel9.msdn.com/shows/Going+Deep/Expert-to-Expert-Brian-Beckman-and-Sam-Druker-Deep-Entity-Framework/)
The main take-away for me is that EF is a strong and well thought out technology for use in the data access layer's of applications. It's another case of MS thinking outside the box. They didn't just create one more O/R mapping technology. They created foundational technologies that address the root issue and provide significant benefits.