I did MVC 2 two years ago. I am now using MVC 4 and would like to confirm a few things (StackOverflow is down for maintenance just now for about an hour).
In MVC 4, we do not need to create a ModelMetadata class to annotate with data annotations for data validation. We may simply annotate the model classes themselves.
In other words, if we are using the EDM generator to generate a model and corresponding classes for us, then we may create a new set of partial classes with the same names and use data annotation attributes on those partial classes themselves.