@model IEnumerable<Guestbook.Models.DataModel.Review>

<table>
...
... рендеринг таблицы
...
</table>

<div id="addReview">
   @Html.Action("Add")
</div>

@model Guestbook.Models.DataModel.Review

@using(Html.BeginForm("Add", "Reviews", FormMethod.Post))
{

<div class="editor-label">
   @Html.LabelFor(x => x.UserName)
</div>
<div class="editor-field">
   @Html.EditorFor(x=> x.UserName)
   @Html.ValidationMessageFor(x=> x.UserName)
</div>

...

<button type="submit">
   Сохранить
</button>

}

public class ReviewController
{
   public ActionResult List()
   {
       var list = Repo.GetReviewList();
       var model = MapTo<Guestbook.Models.DataModel.Review>(list);
       return View(model);
   }

   [HttpGet]
   public ActionResult Add()
   {
       return PartialView(new Guestbook.Models.DataModel.Review());
   }

   [HttpPost]
   public ActionResult Add(Guestbook.Models.DataModel.Review model)
   {
       if(ModelState.IsValid)
       {
           var dto = MapTo<ReviewDto>(model);
           try 
           {
               Repo.AddReview(dto);
               Uow.Save();
           }
           catch(Exception ex)
           {
               ModelState.AddModelError("", ex.Message);
           }
       }
       return PartialView(model);
   }
}