The most important thing I look for in movies is a personality, or some evidence that a human being made it. It's all the better if it's a recognizable personality, with some kind of visual or tonal mood that carries over from film to film; in that way, it's like re-visiting with an old friend. If that's not available, I'd at least like a good idea in a movie. If it looks stamped out of a machine, or molded out of someone else's recycled ideas, then it's not as interesting to me. Failing all this, what I appreciate in a movie is good fun, and that usually relegates the movie in question to "B" status. Hardly anything that's "important" is also "fun." These films are usually associated with bodily responses (suspense, titillation, laughter, etc.), rather than intellectual responses, and so it's automatically assumed that they're not "smart" or "good." (Iron Man 2 is a case in point.)
Fortunately, there are several pretty good "B" movies out right now. Atom Egoyan's Chloe (53 screens) is a fun example of a "sex" film. They used to be called "nudies" (often set in nudist camps) until Russ Meyer took over the genre in the 1960s, and made the films oversized and outrageous. In later years, after the rise of HIV and AIDS in the 1980s, eroticism was often combined with suspense, as if anyone who enjoyed sex was automatically either a killer or a target. Such is the case with Chloe; unfortunately, Egoyan's fans expected something a bit more intellectual than this, but I like the movie's combination of brainy and ridiculous, not to mention that Egoyan usually doesn't shy away from anything steamy (see Exotica and Where the Truth Lies).