Radiant is the blood of the baboon heart is one of the best finales ever. It completely sticks the landing and is a worthy conclusion to a 20-year running, story-heavy series like the venture bros. Only problem is it fucks up the entire series by introducing a plot hole.
The end of the very first season of the Venture Bros transforms the show from a goof-of-the-week Johnny Quest parody into what the show would be really known for -- a lore rich, serial-format show with lots of mysterious backstory. The episode introduces the two core concepts of the show: Dr. Venture has access to cloning technology and willingly uses it to clone his sons when they die, and that he himself is a brother, having swallowed his fraternal twin in the womb. Both of these revelations set off a series of mysteries that don't wrap up until the final moments of the movie.
However, it's teased in season 7 that the Monarch and Dr. Venture are actually at least half-brothers (And their dad was a colossal dick). The movie clarifies this, picking up on a hanging thread from a few seasons back: Rusty is also a clone. The technology they use to bring his sons back to life, his father also used on Rusty when he died on their adventures. Hence, the Dr. Venture we follow was not born in a womb, he was grown as a teenager in a pod. However, this directly contradicts Jonas Venture Jr.'s existence, since we saw him swallowed in the womb. If Dr. Venture really is a clone, he could not have been the one who swallowed Jonas Venture Jr. That body that Jonas Venture Jr was in should have died decades ago, with Jonas Venture Jr.
Oh well, fucking incredible ending to an incredible show either way.