Ever since I first saw the trailer way back last year, this has definitely been on my list of movies to see, and I just want to say, I was not disappointed!
To those considering, I would seriously recommend you see it. It truly goes in depth to explore a holiday that's rather misrepresented and overlooked by those who do not celebrate it. Too often is Dia de Los Muertos wrongly put out as "Mexican Halloween" and its concepts appropriated to mere costumes (the sugar skull makeup), and this is a breath of fresh air of showing how much meaning it truly carries in Mexico.
Along with this, The Book of Life also does a great break of the old "love triangle" trope. Though it may seem like it in the trailers, Manolo, Maria, and Joaquin's friendship is not broken nor is it made awkward because of the romance going on. Maria makes her preference clear, and being a truly strong female character, she makes it clear to Manolo and Joaquin that she is not a mere prize to be won. Following through with this is that, though both of them carry feelings for her, Manolo and Joaquin respect her choices, as they won't let their friendship be ruined by something so petty. (It's also a breath of fresh air to see Joaquin's character be a good example how someone can be cocky without being completely asshole-ness).
In terms of other messages, the film also explores toxic masculinity (showing that saying sorry doesn't make you weak), animal cruelty in bullfighting, and that sometimes though parents want the best for us, they can be wrong and don't get to decide your life of you.
The only complaint I really have is that I feel like the film was a little rushed. But that's just me. Overall, the film's animation is great, the character development is excellent, the plot is awesome, and it's a total 10/10 recommendation.
Now I hope I won't have to wait too long to see Big Hero 6.