It is of course important to mention first off that this is not your standard movie. For a movie going audience conditioned by such spectaculars as Harry Potter, Titanic, Star Wars, and Spider-Man, it would be hard to imagine exactly how this would play out in the theaters today (as I recall, it didn't fair to well back in 1973 either).
All of this doesn't mean this isn't a -good- movie. It contains a lot of sweeping ocean scenery, with of course lots of wonderful footage of seagulls. It also has the great score by Neil Diamond, and then woven throughout this is the original story by Richard Bach. And it is perhaps in that order that this movie exists. It is a relaxing, calming, as well as uplifting (on a very subtle scale) experience. To watch it with the same rapt attention that you might a modern "spectacular", you would no doubt be quickly disappointed and bored. Instead, it should be watched at a time when you just want to relax, no pressing chores calling your name, and no interruptions that you might need to deal with. You might think of this as the closest thing to a full-body massage for the mind, encapsulated in a hour and a half movie.
One caveat however, is that I would recommend that you read the book first, because there are times when exactly what is going on with the seagulls is a little confusing, and difficult to figure out from what happens on-screen.
While I doubt it will ever happen, I would love for this to be released on DVD, it would greatly improve the quality of the video and soundtrack (both copies I've seen of this movie have had an mildly distracting "tracking" problem which results in pops and crackles in the audio), and it would perhaps also allow supplimentary audio tracks with discussions from Richard Bach, Neil Diamond, and perhaps others associated with this film (Hall Barlett, the director died in 1993).