The idea of forms was very abstract and it wasn't clear enough to be accepted, un criticized. One criticism I do think is valid is that Plato does not make it clear about whether the ideal form is of a certain animal, a species or breed. In much the same way, a stick is a meter long because it has the same length as the Standard Meter, or to weigh a kilogram because it weighs the same as the Standard Kilogram.
It is neither eternal in the sense of existing forever, nor mortal, of limited duration. Aristotle stated that, for Plato, all things studied by the sciences have Form and asserted that Plato considered only substance to have Form.
Splitting the existence into two realms solved the problem of permanence and change. Is it still a meter long? The absurdity demonstrated by this and other similar examples is partly what led the earlier Greek philosophers Parmenides and Zeno to question whether we can talk about plurality of objects in the first place.
For Parmenides there is only the One; for Plato, there are many ideas. To a certain extent these criticisms are valid, but in other ways they are not.
Systematically Interconnected - The forms comprise a system leading down from the form of the Good moving from more general to more particular, from more objective to more subjective. The theory of matter and form today's hylomorphism started with Plato and possibly germinal in some of the presocratic writings.
One of them is to reconsider the principle of Separation and what it implies.
We come here to a difficulty which has troubled many philosophic theologians.