It's mostly entertaining, though formulaic in the '70s way where every episode is practically its own alternate universe. (Really, what are the odds that the same reporter would continue to just accidentally stumble upon supernatural occurrences while on routine assignments over and over again, and would be just as disbelieved by his editor and the police every single time no matter how much evidence he uncovered? It often felt less like a continuing series than like an anthology of variations on the same premise.)
But there are a couple of things that don't hold up today, primarily some disturbing, hopefully accidental echoes of racist practices in early episodes. In "The Zombie," Kolchak defeats a black zombie by essentially lynching him, and in "The Vampire," he defeats the vampire with a gigantic burning cross. Why did it need to be on fire? If it’s the holiness of a cross that makes it potent against the spawn of Satan, then surely desecrating a cross by burning it would weaken its effect, not strengthen it. It's a bad idea to show your hero defeating evil by acting like a member of the KKK, especially when his birth name is already Karel Kolchak.
The show also doesn't treat female characters very well, tending to relegate them to the role of victims or beauty-obsessed villains, and Kolchak fat-shames Beatrice Colen's character, whose build is perfectly average. And it doesn't handle Native American culture and lore any better than any other '70s show.