Othello, which presents the personal, inner torments of its characters, is a tragedy in the traditional sense as the hero has a most fatal flaw, in this instance Othello's jealousy which, when combined with Iago's scheming and Othello's honor system and all it represents, serves to offer a tragic tale of misplaced trust and "one that lov'd not wisely, but too well." (V.ii.347)
Expectations of a tragedy include the realization by the fallen "hero" that he has committed a heinous deed or crime and Othello "a malignant and a turban'd Turk" (356), in the eyes of a Shakespearean audience, redeems himself as "nought I did in hate, but all in honor"(297). He then kills himself basically to avenge Desdemona's murder.
Tragedy traditionally contains spirits and superstition or affairs of State and the tragedy is a universally felt catastrophe which affects many characters. Othello, whilst a far more personal account is universally felt because it reveals emotions that every person can relate to and Shakespeare's audience would have been all too aware of the misunderstandings that accompany jealous feelings. Any audience can also relate to characters like "honest, honest Iago," with no apparent motive for such evil but the capacity to manipulate people and circumstances to his own gain.
Iago's ability to mould several characters at his behest whilst appearing to be most trustworthy is typical as it is his actions that reveal the fatal flaw of the otherwise noble and distinguished soldier Othello.