If all you want to do is unzip the contents of a file to a folder, and you know you'll only be running on Windows, you can use the Windows Shell object. I've used dynamic from Framework 4.0 in this example, but you can achieve the same results using Type.InvokeMember.
dynamic shellApplication = Activator.CreateInstance(Type.GetTypeFromProgID("Shell.Application"));
dynamic compressedFolderContents = shellApplication.NameSpace(sourceFile).Items;
dynamic destinationFolder = shellApplication.NameSpace(destinationPath);
destinationFolder.CopyHere(compressedFolderContents);
You can use FILEOP_FLAGS to control behaviour of the CopyHere method.