Short answer is yes.
Kant tried to cut off most of traditional metaphysics as speculative, ie. making assertions about something we cannot actually know anything about.
Basically, the Kantian critical paradigm is that all knowledge (even of ideas that we can never actually experience themselves) is based on experience and that all ideas (or content) has to be validated by or on the basis of experience, not the other way round (Prolegomena, 4:473f. fn.).
The main thrust of the critical idealism is that ideas or assumptions that have no direct correspondence in empirical experience need to be established as necessary for the possibility of some empirical experience via deduction ('transcendental') or it will remain problematic.
In other words: Just because we think the concept of circles and spheres are perfection and heavenly bodies are perfect, they have to be circular and spherical, that inference is null and void if either of the premises is not empirically valid. Validating either perfection empirically is pretty hard, and there is no way to infer the actual shape and properties of objects that cannot possibly be experienced from empirical experience.
On the other hand, one should keep in mind that this is for objects only, not constructs. Kant is perfectly fine with construction purely a priori, like in mathematics. And he also wrote that when we got a science proper (built on transcendental principles a priori - which have to have an empirical grounding), you couldn't fail in constructing knowledge about objects from there on - like in an axiomatic system. His philosophy of nature is not exactly one of his stronger sides though, even if it puts forward some interesting ideas.