PC Magazine has published a review of the new version. MSE offers good basic protection when complimented with best practices.
Microsoft Security Essentials 2.0 — PC Magazine Review
QUOTE: Technically the product name is still just Microsoft Security Essentials, but the About box clearly shows a version number beginning with 2.0. This version has a few new features. It can automatically ensure firewall protection by enabling Windows Firewall if necessary. In Windows Vista and Windows 7, Microsoft Security Essentials’ new network inspection system adds specific protection against network-based attacks. The app also claims better malware-fighting skills, though in my testing it seemed little improved.
* Pros — Simple user interface. Insulates user from confusing details, while making details available if desired. Good ratings from independent labs. Free.
* Cons — Protection weaker under Windows XP. Mediocre results in hands-on malware blocking and malware removal tests. Left some threats running after alleged removal.
* Bottom Line — If using a Microsoft product gives you a warm, safe feeling you may consider relying on Microsoft Security Essentials for antivirus protection. The independent labs give it good ratings, for the most part. In my own testing, though, it didn’t shine. Other free products offer better protection.