The first image can set an expectation for everything that follows. When reviewing a portfolio carrying the name Ann Martin, pause at the opening frame and write a brief prediction about the group. Your prediction might concern its pace, visual density or use of contrast. Base it on what you can see, without assuming a particular subject specialism.
After viewing the complete selection, return to that prediction. Did the opening prepare you for the sequence, create a useful surprise or make a promise the other images did not pursue? An opening can be effective without being the most striking individual photograph. This comparison helps you assess the organisation of a portfolio separately from the strength of its component images.