I'd give 9 out of 10 if I could, but alas, we don't have that level of detail, so 4 out of 5 it is.
Jenna Moran's style is a natural fit for a children's book, and so Invasion works very, very well. Even so, the expected mind-bending perspectives that Jenna's fans so dearly love remain present, so I certainly enjoyed it. In particular, the art style helped the story immensely, the one building off of the other, to the point where I had to stop and appreciate the art to really grasp the full intent of the story, which represents an additional layer of mind candy.
Said differently, page one let me think it was a child's book. Page 2 made me quirk an eyebrow. Page 3 made me do a double take and flip back to page 2 to check the shift in art style.
So why four out of five? Format. Invasion is not a book that you'll want a PDF of. It just isn't. It's a book that you'll want on your shelf or sitting on your table so that your friends can pick it up and page through it and do the same double take you did when you first read it. For $4, it's certainly worth your money, but frankly, I think it would be better to pick it up from Amazon.com so you can amaze your friends and frighten your enemies with it.