A Sprint Review should look at what has been done and what remains to be done. It is quite separate from planning.
The activity you have highlighted is sometimes referred to as "backlog grooming", and it is increasingly common to have other backlog grooming sessions *before* the sprint review, so there is enough time to remove any impediments (e.g. inadequate user stories or acceptance criteria) prior to planning.
I recently wrote an article which touches on this matter:
"Sprint Reviews in Practice": http://agile.dzone.com/articles/spr...s-practice
Hope this helps.