I've heard some describe it as "heretical" but I fail to see how. I think Molinism is a fine theological opinion, and I've certainly used some of Molina's arguments when dealing with both Arminians and Calvinists.It's not exactly "heretical" but I don't see it being compatible with our faith tradition.
It's certainly grounded in Scholasticism which isn't directly part of the Orthodox mystic tradition...but then again, I don't bear a torch in the anti-scholasticism lynch mob. I think scholasticism is very useful, as long as we don't let it cloud our vision and we always remember that our ability to reason still ultimately falls short of the ineffable mystery of God.
As long as we remember to stand at awe, instead of trying to define and dissect that which exists beyond our ability to reason, I have no issues with scholasticism and see no reason why people can't maintain views such as transubstantiation, Molinism or other scholastic teachings...as long as we don't make them doctrines and realize that such reasoning and cataphatic theology has its limitations.