My first thought is that this is a pussy move by Congress, and Obama is correct to veto it.
If Congress thinks Saudi Arabia is responsible for 9/11, then pass a resolution with sanctions, demanding action by Saudi Arabia (imprisonments, compensation), or even declare war if they really think that. This "let the families sue" seems like a cop out to me, a shirking of their duties.
If Congress really wants this to pass, put it to a vote (the veto override vote), and make the Congressman put their names down as for or against.
I honestly don't see this as a partisan issue, but since the bill passed by unanimous consent, it will be interesting to see which Democrats vote to override Obama.
Link: http://www.cnn.com/2016/09/23/politics/september-11-bill-saudi-arabia-veto/