Put simply, Locke is an underrated film that features one of the most underappreciated performances of all time, courtesy of Mr. Tom Hardy. It's not often that you can point to a movie that works solely because of one performance. Sure, there are films that are elevated from "good" to "great," or from mediocrity to legitimate quality, but it is a rarity to see a film that features an actor who quite literally brings the character into the real world. Hardy's heart-breaking, but also mind-blowingly authentic performance transforms what could easily be a film trying to profit off the gimmick of only showing one man in a car for the duration of the runtime into a captivating character piece.
The plot, though on the surface doesn't run much deeper than a Wikipedia summary, is executed pretty well. Though repetitive at times, it stays engaging for the majority of the film.
In terms of the technical aspects, director Steven Knight does the best he can with the obviously limited settings, with creative lighting and interesting shots out of the window, but such limitations can only hold up for so long. Of course, such barriers cannot be overcome, but the lack of different set pieces does become tedious after a while.
Overall, Locke is an engaging film which becomes wildly elevated by the performance of Tom Hardy.