Complex sentence: Polls and commentators predicted the outcome would be too close to call and would result in a second hung parliament similar to the 2010 election, dubbing the vote' the most unpredictable in decades.
Split into simpler sentences: Polls and commentators had predicted the outcome would be too close to call and would result in a second hung parliament, similar to 2010. Some dubbed the vote' the most unpredictable in decades.