It's quite fashionable, in some fan circles, to be mean spirited about Adric. While this isn't entirely undeserved, it should at least get a mention that, as was noted about Peri, he actually worked quite well with the Doctor with whom he was designed to travel. The Fourth Doctor and Adric just fundamentally work. All the features that make Adric so unbearable later on are still present here, but they're muted in Tom Baker's presence. Adric is still a pretentious, socially awkward little creep, and he's not even one that's terribly well acted. But that actually works in the character's favour since Matthew Waterhouse is so clearly in awe - and probably more than a little afraid - of Tom Baker that it keeps Adric humble in a strange sort of way. This version of Adric clearly knows that the Fourth Doctor would have absolutely no hesitation to chuck him out the door in a heartbeat, and that keeps him from ever pushing it too far. He shows respect to the Fourth Doctor which makes his less enjoyable character traits bearable (and even at times interesting). After the regeneration, that sense of respect disappears completely. Adric, with the Fifth Doctor, feels entitled. As a companion he essentially has the best job in the universe and he spends all his time being condescending to more interesting companions between bouts of whining. That's why the nation cheered when they finally blew him up.