Any success largely depends on the presentation to USCIS. The case officer doesn't know you and they just read what's put in front of them. They have the final say and apparently have alot of discretion in their determination of eligibility. You definitely need to tick certain boxes to stand a chance and prove that it is in the national interest by granting you and your family an immigrant visa. Having said that, I've been approved, submitted all necessary paperwork, and moving asap. There's also a thread over at the North America area on here which might give you more info.