There are points of legitimate criticism of the Pope. For example, there was criticism of his appointment of Cardinal Levada to the CDF.
There are points of permissible criticism of the Pope but I don't see the AQ poster's writing as falling into that category.
The poster you referenced stated that the Pope himself was not "solid" nor "orthodox" enough.
It's one thing to say that some bishops are not "solid" nor "orthodox" (a statement which is indisputably true). It's quite another to say that the reason for this is because the Pope himself is not orthodox nor solid enough. This implies that he deliberately passes over more "orthodox" candidates in favor of weaker appointments.
If you think that applies to Levada, good luck to you. It doesn't mean your criticism is "legitimate", though because you don't know the reasons for the Pope's appointment nor how Levada has discharged his duties in God's eyes. It's permissable to disagree with the Pope on things like the appointment of bishops but to take that the extra step and suggest that the Pope himself is of dubious orthodoxy is to take one of the 39 steps on the road from being respectful and obedient to the Pope to becoming part of the "more Catholic than the Pope" movement.
I don't keep a grade card for the Pope. I have too many problems keeping my own house in order.