Many of us are not aware of the fact that SPMetal only runs against the field type provided by SharePoint Foundation. So, if you use Taxonomy, Publishing HTML, Publishing Image in your list, you will not be able to generate an entity class with these fields by running SPMetal command as it will skip those fields. You can easily overcome this problem by using one plugin from codeplex, “SPMetal Extender”.
LINQ to SharePoint has several limitations; there are various techniques to improve SPMetal code generation. This project provides a Visual Studio extension to allow developers to easily work with list fields that are not covered by SPMetal’s code generation. The extension provides additional functionality to the server explorer to allow the developer to generate code to extend LINQ to SharePoint’s functionality. For example, SPMetal does not generate strongly typed properties for lists fields based on “Publishing HTML” or “Taxonomy” site columns. You can download SPMetal Extender from Here