Kant is famous exactly for the breaking with the tradition of metaphysics that preceded him. His point was that all our experience is about phenomena (appearances), and that "ultimate nature of reality" is inaccessible, if it has any meaning at all. That "rational intuition" postulated by previous philosophers, like Descartes and Leibniz, to break out of this limitation was based on misapplying concepts of experience to noumena, entities that can not be objects of any possible experience. He calls "transcendental illusion" taking "a subjective necessity of a connection of our concepts… for an objective necessity in the determination of things in themselves". And he illustrated, in antinomies of pure reason, that such misapplication is not only a category error, but can lead to contradictions. According to Kant, the purpose of philosophy is elucidation of empirical knowledge that we do have, through critical analysis of its sources, not metaphysical speculation about reality, which does not and can not produce any knowledge. See Kant's Critique of Metaphysics.
Kant credited Hume for helping him so see the light, "it was my recollection of David Hume that broke into my dogmatic slumber", and he characterized his critical philosophy as a "Copernican revolution", writing "let us once try whether we do not get farther with the problems of metaphysics by assuming that the objects must conform to our cognition, which would agree better with the requested possibility of an a priori cognition of them, which is to establish something about objects before they are given to us. This would be just like the first thoughts of Copernicus, who, when he did not make good progress in the explanation of the celestial motions if he assumed that the entire celestial host revolves around the observer, tried to see if he might not have greater success if he made the observer revolve and left the stars at rest".
The main deviation of Kant from Hume is that while Hume denied the possibilty of non-empirical knowledge altogether, Kant pointed out that mathematics or the principle of causality in physics, which Hume criticized most ardently, are treated as true a priori, i.e. non-empirically. However, he sought a justification for this not in metaphysics of "reality", but in our own constitution. His ingenious idea was that we ourselves insert non-empirical aspects into our own experience:"So the Humean problem is completely solved, though in a way that would have surprised its inventor… the complete reverse of anything that Hume envisaged — instead of the concepts (of the understanding) being derived from experience, that experience is derived from them".
What Kant sees as his solution to the Humean problem, as inspired by Hume's Enquiry, covers also a more expanded version of it in the Treatise. However, a century later Husserl, who read all of Hume's major works including the Treatise, and considered himself influenced by Hume and not by Kant, developed a different non-metaphysical philosophy. But it is still in the style of the "Copernican revolution" and analyzing how knowledge is acquired, so it is highly unlikely that reading the Treatise would have changed the major themes of Kant's philosophy.
After Kant philosophers who still insisted on doing metaphysics had to either reinvent it, or to find a new source of metaphysical knowledge. Some notable examples are Fichte, Hegel and Heidegger. "Hegel's project of constituting the world through logic could be read as an attempt to demonstrate that the conditions of the possibility of our thinking of objects are the conditions of the possibility of the objects themselves". Heidegger, and the entire tradition of existentialism, goes further by rejecting the centrality of knowledge to both life and philosophy altogether, because "existence precedes essence". This leads to a very different kind of metaphysics based on direct "insights" into existence. Alternatively, Husserl's version of transcendental philosophy reexamines empirical experience and points out that our perception is not purely sensory, but also involves simultaneous grasping of ideas or forms of objects, the aspect Husserl called ideation. One way or another all successors had to deal with Kant's critical takedown of old metaphysics.