Mostly realistic in most aspects apart from death. Dead characters were almost never mourned or mentioned within minutes of their dying. How often did Jesse, Xander's best friend at the start of the series, get mentioned after the first two episodes?
In many cases just-killed humans simply disappear (the DVD commentaries mention how often dead bodies simply drop out of shot and vanish because they couldn't show a pile of corpses just lying there festering on the network)
It was almost a running gag that the Sunnydale death count put most dictatorships to shame, and yet there were almost never memorials to the deaths, and that despite everything, thanks to Buffy, her graduating class had the lowest mortality rate in Sunnydale High history (and then many more got wiped out less than a week later at graduation)
It's what made the death of Joyce so powerful, since it was one of the few times that actual death of someone was a story, rather than an incidental sideline.