Many think they should skip it because it's not part of the story, but it's a satisfying and visual spectacle with a round beginning and ending that makes you can put it on BEFORE or AFTER S2. (There's a certain scene with Bond that's going to remind you of the last episode of season 2 and this is just one example). They give you all the context so you understand the story from the beginning and the good thing about Spy Family is that it is very intuitive and they explain everything in detail.
Story: A plot that reminds you of how close the Forger family is and how their occurrences motivate them to stick together in a series of unfortunate events (very convenient) but that reinforce their family bond.
This movie mixed the best of the anime seasons and compressed it into one movie, even recycling some moments and phrases, but with another perspective, which makes it more enjoyable and that's why anyone can watch it without having seen anything. It has an absurd but very good comedy as it is to be expected from this franchise, you will laugh in more than one occasion.
ANIMATION: It's probably not that outstanding overall, but at key moments, both Loid and Yor's scenes get excellent animation sequences that you should enjoy in the theater. Even Anya has her "magic" moment which required great animation.
