Personally, what I think are the probably the most realistic things you can view are the videos and photos posted here on SB. Many are taken in places where you might actually go diving and can give you a good idea what it's like, and many are truly excellent. Lots of people have seen my videos of such places as Cozumel, Isla Mujeres, Puerto Vallarta, Hawai'i, and California and were amazed. And my videos aren't particularly great or anything, just pictures of what's down there. It doesn't say where you are located but you can probably do a search here and find some local photos and videos by other members.
One of my all-time, favorite diving movies is Dive to Danger, directed by Bruno Vallati. It covers a very broad spectrum and dispels some of the myths and also exaggerates some of the dangers. I also think the old Sea Hunt series with Lloyd Bridges can be very educational, however it is rather outdated. Many episodes are available on YouTube. Some might find it very entertaining, and others might be bored to death. You can also find amateur videos on YouTube covering just about any dive-related subject you might be interested in. I wouldn't take anything too seriously that I saw in any modern movies, One interesting note about Sea Hunt: the type of diving they/we did back then has regained a lot of interest, for many reasons.