The first time I saw Les Misérables was 9 years ago in London. I went with Emily, who was 10 years older than me and familiar with the story. She loved it. I thought the characters had confusingly similar names, and from the nose-bleed seats, it was hard to tell who was who. Ten year jumps in the plot didn't help and, since I was lost anyway, I decided halfway through I would just try to enjoy the experience of watching a musical play in London. I did enjoy it, but Emily had to explain the story afterward. Going to shows in London with her ended up being one of the most memorable things from my first trip to Europe, along with our Paris room that looked like it had been designed for the red light district, and a late-night skinny dip in the Rhein in Germany with all the girls on the trip. I think I saw Les Misérables another time after that, though I can't remember where or why. Last night I saw the movie (also with a friend 10 years older than me! how poetic!) and the third time must be the charm! I got the plot. Maybe understanding all the words in the songs and being able to clearly differentiate characters' faces instead of looking at specs on a stage from the upper balcony helped, too. I recommend the movie.
I also recommend the PhD comics adaptation: