I have seen the movie, I think the story is quite understandable. Boys' troubled adolescence is linked to an old philosophical problem. "Where have we come from, who are we, and where are we going?" From ancient times to the present, there have always been people who have tried to search for the power that governs everything, or find a way to live forever, but the results have always been absurd and terrible.After rewatching it recently I'd say that it may not be the best anime movie ever made, the plot is a bit messy and convoluted (if you're able to follow all the storylines at first viewing) but I still think it's an absolute treat in animation, its style and tone. The first 10-15 minutes are absolutely jaw-dropping and iconic to me.
The manga does a much better job at presenting the plot, characters and giving a depth to it all and of course its art is magnificent, but the film and manga are essentially two separate iterations of the same concept and basic story. I have to compliment Katsuhiro Otomo for being able to craft the film in radically different ways while he was in the middle of the publication of the Akira manga, instead of trying to cram everything into a 2 hour movie.
I hope you'll enjoy your first viewing, but don't worry if you end up not loving it, its appeal isn't for everyone.