I like watching movies that I liked or found interesting again with audio comments. As directors keep mentioning, they wonder who listens to them, or whether anybody seriously wants them at all. But I don't understand this scepticism. They often are genuinly interesting. When you're really into a movie or franchise, DVD bonus material (or online videos that could have been DVD bonus material) are great to feed a fan's longing for more input. And an audio commentary to a movie is like 90 minutes of extra bonus material. This is why, when buying DVDs I often make my decision dependable on whether there is audio commentary included or not. Recently I've watched more movies' audio commentary in a short amount of time than usual. That's why they're on my mind.
In my mind, there are a couple of types of audio commentary.
Director's Fan Service
This is the most common kind of audio commentary found on movie DVDs. The director talks about the scenes currently seen on screen, gives background information, tells an interesting anecdote from the set, explains the idea behind a scene, talks about difficulties on the way to the final scene, indroduces an actor, comments on a camerapersons creativity, mentions cut scenes, alternative story paths or differences between the original script and the result, thanks somebody for creative input, and so on. There is often some of this in the other types of commentaries, which is good because it's what I'm mostly interested in. Directors usually have more than enough to say to fill a movie's length with more or less constant comments. If not it can be like the following kind of audio commentary.
Director's Mandatory Overtime
If the director doesn't feel like doing the commentary, can't be bothered or for some other reason can't think of interesting things to say it can seem like they were made to record the commentary. Some comments every other scene, some renark inbetween two scenes but half the movie is still playing without any commentary. This can be disappointing and maybe even boring. But it's still so much more than no commentary at all. Sometimes in these cases the commenting person resort to describing what's seen on screen because nothing else comes to mind.
Director's Film Industry Lecture
A solution to not having anything interesting to say about what's playing can be to just talk about whatever the directo feels like talking about. Whose (of their colleagues) work is underrated, what people don't understand about certain classic movies, what they would like to work on in the future, who acts well with whome, practical tipps for other directors and so on. Not what I expect from a movie's audio commentary. But it can be interesting, too.
Director and Actor's Dialogue
My favourite audio commentaries are of this kind. If two to four people come together and watch a movie they have made together, there's certainly enough to talk about. It can be chaotic, harmonic, mostly one-sided or evenly distributed. Because of the extra dynamic those tend to be the most cheerful. They can also leave me wondering what each of the people would have had to tell if they each had had the entire movie's time alone.
Individual Commentaries for Different Departments
When much more than three people are to record audio commentary it makes sense to separate them into two or more commentary tracks. Sometimes teams are separated into departments. For example actors, camera and lighting or costume and set designers record their own commentary. This format is probably especially interesting for people who work in film or are aspecially interested in some part of the production process.
Edited Compilation of Comments
While it is true that producing an audio commentary is an easy way to add long playing bonus material to a DVD compared to producting other types of material, that doesn't mean that no work is put into producing them. Sometimes various people record their comments individually and the most interesting comments are chosen for the commentary track.
Interrupting the Playback
One of the features with which Video DVD was promoted as more useful than VHS and DV was the ability to change the order or selection of video content depending on thhe viewer's choice. This sadly rarely used feature means a DVD can contain several different cuts of a movie or let the viewer decide how a story continues. Only once I saw a DVD that contained the setting to interrupt the movie with clips of the director commenting on the current scene. I forgot which movie that was.
Visual Commentary
Not audio commentary. But it can go along with an audio commentary track. These are DVD dubpictures (little drawings, diagrams, text, handwriting, arrows) that may contain additional information, funny remarks, etc. They are overlayed just like subtitles. But often positioned outside of the movies' imagery, meaning one has to use the player's settings to create black bars and hope that it still renders the additional pictures, which software DVD players don't do.
Fan's Reaction Videos