The criticism Cameron tends to get is two-fold. Firstly he didn't have any clauses whatsoever built into such a serious vote. Either a certain majority % vote being needed, or a majority of the unions voting leave, not just the biggest deciding for everyone else. Either of these clauses, or any others, aren't required, and rarely happen in other votes. The other unions being small compared to England is just part of why a Union like we have is seen as failing by many.
Secondly, the half-hearted, flip-floping and utterly dreadful remain campaigns carried out in the UK, mainly by the Conservative, and Labour, are more what people are furious about. So many leave lies were allowed to foster. Half the Conservative party was back-stabbing the rest (as was Labour), and then a remain "campaigner" in May, charges in to become PM, and then suddenly becomes Mrs Hard Brexit. All while Corbyn a Euro-sceptic tried to convince everyone he was remain, and then now in the wake of Brexit is like a fucking ghost at offering opposition to May.
Most people are more irate about the second part, not so much the first. It's democracy, the second is our usual MSM lies, propaganda, the UK fear machine and political parties like the Conservatives and Labour being a fucking mess.