IHttpActionResult

This is new feature to WebApi 2.0 In many ways this is similar to action result in asp.net mvc. There are some build in action result like mvc controller has view result, json result etc. Web api has OkResult, NotFoundResult, ExceptionResult,UnauthorizedResult,BadRequestResult, ConflictResult,RedirectResult,InvalidModelStateResult.

 
  public IHttpActionResult GetDetails(string name)
        {
            Product product = _productService.GetProduct(name);
            if (product == null)
                return NotFound();
            return Ok(product);
        }

This simplifies unit test, for example if you are using request object to create http response object then you need to do setup to unit test controller.