Keith A. Mathison, author of The Shape of Sola Scriptura, has a great article discussing the problems of the apologetics and theology of Cornelius van Till, including his piss-poor understanding of the Trinity:
Christianity and Van Tillianism
While it is a lengthy article, it shows that, even from a Reformed Protestant perspective, Van Till's apologetic is very problematic.
On the issue of Reformed presuppositionalism, see the podcast episode I did with Joseph Lawal:
Episode 18: Joseph Lawal (LDSPhilosophy) on the Problems with Presuppositional Apologetics