Whatever your opinion, it can never be argued that Act 1 is not of great significance and importance to the play 'Othello'. This act uncovers many clues and vital details of the plot and the characters that help us to build our understanding of the play in later scenes, and also form our opinions and feelings of certain characters. .
The first vital piece of the plot we discover in this act is Iago's feelings for Othello. We quickly learn of his hatred of him due to the fact that he has been passed over for promotion by Othello, who has awarded the lieutenancy to Michael Cassio - a much less experienced soldier. This stems further causes for hatred, such as the apparent rumour that Othello has 'cuckolded' Iago (slept with his wife) which Iago decides to hold against Othello, even though he clearly states that he does not believe this rumour to be true. Already, even in this first scene, Iago's true colours are shining through. .
I also personally believe him to be jealous of Othello's marriage to the beautiful Desdemona. Iago seems determined to break up this marriage even before his later, more detailed and clever plans are formed, and he stirs up Brabantio's anger with crude references to Othello 'tupping your white ewe' - an unflattering reference to the sexual relationship between Othello and Desdemona. Already it is becoming evident that Iago is crude and unable to understand love and loving relationships. This idea is developed later in the play, but it is in Act 1 that it I first suggested to us. .
Without Act 1, we would also be unaware of 'the shaky foundations of the relationship between Othello and Desdemona' as the second critic says. This is a very important factor of the plot. Othello and Desdemona so not have the typical good foundations of a marriage. It seems Desdemona has fallen in love not so much with Othello, but with his past and the idea of what he represents - his bravery and his travel, his worldliness.