I adored the graphic novel adaptation of The Son of Neptune so I had high hopes for The Mark of Athena. Unfortunately the adaptation just isn't as good. 

It's a great story of course (with honestly the best ending of any Riordan book) and the art style is decent. My main issue comes from how much essential plot has been either trimmed down drastically or cut entirely, to the point that I'm genuinely unsure if someone unfamiliar with the original novel will fully understand what is going on. Some events are shown in pictures but not really even referred to in the text at all. There was one point in particular where I was rereading the text and examining the pictures, trying to figure out how I'd missed something important happening. 

I did enjoy the book, it was a fun, quick way to reread the story and I had a good time with it. I just wish this adaptation had another 50 pages to really give it a chance to be great.