Period detail is underwhelming and sometimes downright inaccurate. But the show itself is pretty decent. More glossy than gritty, though.
The series opens in 1977, but in the first episode the main character and his girlfriend go the movies to see a film that left the theaters 2 years earlier ("Dog Day Afternoon"). And when driving in a car in 1977 the radio plays "Hold The Line" by Toto, a song that wasn't released until late summer 1978. I guess most people who aren't old enough to remember that won't notice or care. And ultimately it's probably not that important. But it robs the show of its attempt at time-period authenticity. And the fashions of the day are underrepresented, perhaps because they'd be too distracting. But ignoring them is distracting too.
I know that shows like "Mindhunter" (FBI profiling, hunting killers, etc) is a popular genre. But with so many of them over the years you soon start to notice the difference in quality.
My personal preference is the 1986 Michael Mann film "Manhunter", which featured the first on-screen appearance of the Hannibal Lector character (though his name is spelled differently in that film than above).
"Mindhunter" is decent enough, but I think the disregard for authentic period detail harms the project.