While it might anger me some of the changes they made for the musical, I can accept the reasonings behind them (which I read about this evening in an article in the BYU Magazine). The main themes of the book as well as the musical are forgiveness, love, and redemption--God underlying all three.
To condense the 1400 pages and scads of characters, some of the latter had to be left out. Minor stories make sense. But in getting rid of of the minor one related to Max and Valentine, you lose the theme of love. The musical kept a smaller version with Albert and Valentine, but it's not quite the same. We needed to see it somehow more strongly connected with Edmond Dantes. Thus the rewriting of Mercedes' character and story.
I liked the musical's focus on redemption. I loved that Dantes had an entire song to realize that he was wrong, and that when he sang that word redemption, it was so full, top of voice, and vibrantly strong--exactly how I feel when I think of how my Savior has redeemed me. I love it when music matches and then enhances our capability to express our emotions.
Here is a video so that you may hear Dantes' song (with redemption at 2:23--which I'm pretty sure our guy held out much longer). While I'm coming to love the music the more I hear it (as is usually the case for me--takes me a few tries before I finally click with songs), it is such a shame that you cannot hear it sung by our Dantes. He (and our Mercedes) were magnificent.