One of the better. Does what you'd expect. Has the usual toolbox of added blocking functions. Relatively easy to use. I have this and PC Tools Spyware Doctor and Lavasoft's Ad-Aware and it's pretty much a wash as to who's better. It depends on your interface preferences, I guess. I lean more toward Lavasoft Ad-Aware SE Professional.
As with all anti-spyware, it doesn't catch it all, so more than one doesn't hurt.