This is the earliest of David Cronenberg's films that I've seen, from all the way back in 1981. The progress of Cronenberg's career is an interesting one; he started with relatively straight body-horror movies like this one, eventually began using those horror elements to pursue more intellectual questions in films like eXistenZ and Spider, and by now has moved on to abstract, almost purely intellectual films like A Dangerous Method and Cosmopolis. While the middle-period movies have probably been the most interesting overall so far, there's still something to be said for the more straightforward earlier work.
Scanners might well have set a new standard for horror violence in movies in 1981; I certainly can't think of anything earlier that can beat this film's head-explosion scene. The plot of the movie involves "scanners," who are a group of powerful telekinetic people capable of harming and even killing others with their powers, but who usually don't really know how to master said powers. We follow one particular scanner (Stephen Lack), as he is recruited by a scientifically-oriented corporation to track down and stop another rogue scanner (Michael Ironside).
The characters in this movie are pretty boring, except for Ironside's villain Revok. He's by far the most memorable presence in the movie, and it becomes much more entertaining whenever he's in it. Stephen Lack is rather wooden as the protagonist, and Patrick McGoohan's scientist Dr. Ruth (not that Dr. Ruth!) is too confusing to really be interesting.
The movie is a decent example of how to do science-fiction/horror on a low budget. Many of the "scanning" are accomplished simply through acting and sound effects, and it's generally quite effective and visceral. The outbursts of violence are relatively rarer than you might expect, but they are definitely gruesome and memorable when they do happen. I guess the main disappointment here is that, compared to later Cronenberg films, there isn't all that much to it beyond the gross-out effects and the sci-fi concept. The characters are pretty bland, and Cronenberg doesn't really use the material to ask any larger questions. It's maybe a little unfair to read this movie retrospectively through the lens of 32 years of later Cronenberg work, but oh well. It's got its moments, and one particular scene is both genuinely surprising and hilarious, but compared to much of his other work, it's a little basic.