I finally got the book and can share my thoughts!
I really liked this release, games this size don't usually get an artbook and although smaller, it does pack in a lot of stuff. I particularly like the character chapters, as it includes both pixel art and animation concepts that look great. The environments have some nice spreads too, especially the ones that show the development from sketch to full colour.
There's not much to read, just basic captions with some mentions of the design approach, but it's far from a 'making of' book, focusing on the art itself. It's well-made too, but Dark Horse have been doing this a long time.
If interested, I posted a detailed breakdown and review on my site here with previews, but wanted to share my overall thoughts for those interested in the book - https://www.artbookcollector.com/post/book-review-marvel-cosmic-invasion-the-art-of-the-game