I think that this is an interesting topic. You might have to do some wide ranging thought about it, but there are some fundamental similarities present. On one hand, both are struggling with success. Othello has reached the pitch of prosperity in being a named a governor and is married to Desdemona. He has a difficult time in embracing this success as something reflective of him and being secure with it. Insecurity and doubt creep in as he experiences the zenith of success. Gatsby has acquired great wealth and has conceived an image of success with the material trappings to support it. However, his reckless pursuit of Daisy is one where destruction is the only plausible end, and his failure to recognize these elements brings about his own end. Another similarity is both of them fail to find spiritual or ethical counsel in another. Othello is completely led astray by Iago, and while Gatsby respects Nick, he fails to really listen or heed much of what is possibly said in counsel. Neither one of them is able to receive proper advice. Perhaps, a case can be made that neither one of them are in a position to receive such advice. Yet, it is notable to see both of them operate in a capacity without any real spiritual or ethical adviser. I think that one definite difference between both is that Othello has the woman of his initial dreams, while Gatsby is in pursuit of who he thinks she is. Another difference is that Othello recognizes his own failure and his own shortcomings, while Gatsby is killed before he is able to do so.