The most important measure is how well he weaves his core principles stated here into how Facebook makes its money (the way Jobs did with Apple).

More specifically, I worry that Internet.org is an advertiser-funded competitor to the user-funded internet as we know it, and that the interests of advertisers are in many ways contrary to the interests of individuals (e.g. w.r.t. privacy).

Information pipes are a really important building block to a thriving political and economic ecosystem, and for those blocks to be sturdy, it's important that these pipes have built-in privacy protections which remove a lot of value advertisers derive from them.