Is the content appropriate to your information needs. A subject directory organizes lots of sites for ease of access. The Argus Clearinghouse from the University of Michigan's University Library and School of Information and Library Studies, is a collection of subject-oriented guides to the Internet covering subjects from neuroscience to theater. Michigan Electronic Library from the MLink Project, a public library maintained at the University of Michigan. Access to reference links of all sorts from science to entertainment.
Search engines are a little more complicated.
Also remember, all of these search engines work in slightly different ways. For this reason, it's often a good idea to use more than one to find what you want. Don't forget to read the help screens to get a better idea of how to search. It can do simple or complex searches and is very comprehensive. It also lets you do some specialized searching.