Gatsby's wealth has come from dark dealings and associations with shady characters like Meyer Wolfschiem. However, when Nick says to him, 'They're a rotten crowd..you're worth the whole bunch put together' it suggests despite this, he is seen as more virtuous than other characters; 'rotten crowd' and 'whole bunch' refer to other rich characters whose wealth comes from old money like Tom and Daisy Buchanan and Jordan Baker.It also refers to all the people who flock to his parties, not a single one of whom shows up to his funeral. He is better than all these people because he is not interested in wealth for its own sake but only so far as it alllows him to achieve his dream of winning back Daisy. The 'rotten crowd' only understand the American Dream in terms of money and a rich lifestyle; Gatsby instinctively understands that it should have a spiritual dimension as well.
The fact that Nick considers his dream as 'incorruptible' also places Gatsby on a higher level. Gatsby could have any woman he wants but he remains loyal to Daisy.