The images taken by Pioneer 10 and 11 were of much lower quality than those of later planetary probes. I wonder if this is representative also for their other instruments. For example, they don't seem to have discovered volcanism on Io or any rings.
Should the Pioneer 10 & 11 be considered as disappointments or poorly designed missions (maybe prematurely rushed for prestige in the space race)? Or were they the necessary groundbreakers which made the Voyagers so successful? Was there really a big gap in science results (and interplanetary probe technology) between Pioneer and Voyager in the mid-70s and if so, was the reasons for it just general technological maturity, or some change in mission design philosophy at NASA?
I rarely see the Pioneers mentioned, while Voyager is still often admired even after the Galileo and Cassini orbiters. The first two (out of only seven to date) probes to the outer planets seem to have missed the spotlight in space exploration history.