Underrated!
Wow, I can't believe this movie has yet to be discussed on here! Re-watched this with my little sister tonight. I grew up reading these books, and was very pleasantly surprised at how great this movie turned out. This and Speed Racer might be the only childhood favorites that got good film adaptations..
The things I like most about the Captain Underpants Movie are:
1. Just how close it really is to the source material. The plot essentially the 1st and 4th books mashed together, but the rest of the movie is littered with references to the first 6 or 7 books.
2. It looks as though the movie might take place in the late 90s, when the first book released. Any technology you see throughout the school is dated (CRT TVs and computer monitors, VCR in Krupp's office, etc.) This could be an homage to 1990s Captain Underpants, or a joke about Jerome Horwitz Elementary's refusal to actually use their budget on anything educational.
3. The art-style is spot on, and Flip-O-Rama even makes an appearance!