New genre: Completely engaging, without being overtly preachy.
There are movies that preach. Unabashedly preach. Deepa Mehta's Fire as well as Water, for example. There are movies that are completely engaging, which don't really preach at all. (too many in this category).
There are also films that sometimes get so wrapped up in their preachery, that they get obscenely obfuscatory (read:Hey Ram!).
Then there are films that remain flat center at the middle of the philospectrum. Movies with high preach-potential, but still remaining engaging enough for the viewer to remain tensely involved. Basically subtle-crucial messaging through a brilliantly gripping storyline.
Two movies that achieved this superlatively in recent times were Rang De Basanti and Guru.