New features in NuGet Package Explorer 1.0
1. Compatible with NuGet 1.2
Package Explorer 1.0 can open packages that are created by nuget.exe 1.2. (Previous versions cannot due to a breaking change in the .nuspec schema.)
2. Support adding GAC assembly references
NuGet 1.2 adds support for setting references to GAC assemblies in the .nuspec file. Package Explorer 1.0 allows you to set them in the package metadata editor.

3. Support opening .nuspec files directly
In addition to .nupkg file, Package Explorer 1.0 also allows you to open .nuspec files directly. It is as if you run nuget.exe on the .nuspec file and then open the resulting .nupkg file, but now Package Explorer saves you from the middle step. Sweet, eh?
4. Export package to files
Think of this as the reverse operation of packaging. When you have opened a package, say from the NuGet feed, you can choose File – Export, and then specify a folder. Package Explorer will then export all the content files of the package to that folder,
including the .nuspec file.
5. Syntax coloring for the content viewer
The content viewer has been enhanced with the syntax coloring capability, thanks to Drew Miller’s awesome
ColorCode library. It supports most common languages. A picture is worth a thousand words in this case.
6. MRU list
There is now a MRU list under the File menu which keeps the 7 most recently opened packages. It works for both local packages and online packages.
7. Various bug fixes and UI enhancements
This release includes various bug fixes, UI enhancements and performance improvements.