The knowledge base was impressively huge but it also took a lot of work to learn because at the lower levels it was extremely abstract. A lot of the assertions in the KB were establishing very low level stuff that only made sense if you were really into abstract logic or philosophy.
They made bold claims on their website for what it could do, but I could never reproduce them. There was supposedly a more advanced version called ResearchCyc though, which I didn't have access to.