The curse of being a "Venture Bros." fan is that a big part of the show's charm (at this point) is the way it's gradually turned making fun of the self-referential moebius-strip nature of comic books and "cult" genre series (OMG! This suddenly super-prominent character was in the background on that random flashback three seasons ago!) into a functioning continuity that's rewarding in it's own right... which becomes REALLY hard to keep track of since there are such lengthy breaks between seasons.
Fortunately, since the break between seasons 4 and 5 (debuting June 2nd!) was longer than usual, Adult Swim has posted this compressed recap of the important-ish stuff - though what I'm most excited about is the apparent Season 5 returns of Captain Sunshine and Ghost Robot (a ghost living inside a robot, which we are told is completely different than a machine with a soul.)