The introduction is a justification for why the study was conducted.
By the end of the introduction you should have a very good idea of what the researchers are going to study, and be convinced that the study is absolutely necessary to advance the field.
The justification should be a combination of improving on previous research and good theoretical reasons and practical reasons for why the study is important.
If the authors are talking about a controversial issue, are they presenting both sides in a reasonable way? Is their choice of one side over the other based on hard evidence?
Do you understand what their hypotheses are e.g. what they expect to find?
It is not good enough just to say that the study has not been done before. There are plenty of topics that have not been scientifically researched before but that doesn't mean that they should be. For example, I doubt that anyone has ever looked at the correlation between favorite color of Skittles and personality, but that doesn't mean that it should be researched unless there is a good theoretical reason for why we would expect a relationship and a good reason to think that knowing the relationship would advance our understanding of personality in some meaningful way.
