Iron Lady was the answer. War Horse was so filled with cliche that you knew what was going to happen at every turn, and your anticipation was never wrong. Will the horse and his boy ever meet again? Well, what do you think? I don't want to give the plot away, but every plot question was answered in exactly the way you expected.
Iron Lady, on the other hand, had the clever device of switching between Margaret Thatcher in the present (elderly, with the onset of dementia) with her incredible history. You may have known the history, but you didn't know the present, nor when there were going to be parallels between the past and the present, nor when the switch was going to happen.
When we read, we often anticipate the ending - the guy gets the girl, the murderer is uncovered, the jewels are found and restored to the rightful owner. Anticipating the ending doesn't matter; in fact, we'll be disappointed if we don't get the answer we expect. What we enjoy is not going the route we were expecting, but still ending up in the right place. That's the trick of story telling: giving us what we expect but not in the way we expected it.