Though it's hard to imagine television being more culturally significant anywhere than it is here in the USA, it's no trouble picturing it being a whole lot better. In England, TV shows are frequently both; the noncommercial nature of BBC programming and the cross-class appeal of the medium are important factors. Plus, British shows feature longer episodes and shorter seasons. And, as pointed out by Anthony Horowitz, writer/creator of Foyle's War, Midsomer Murders, and other programs, the figure of the detective (more common on UK TV than any other type of drama) is central to the British psyche--only with the provocation of the nosy outsider is the English predisposition toward emotional reserve challenged.
The best is plainly Foyle's War. Like most British detective series, it's set in a provincial town, where the detective--in this case, a police inspector played by the great Michael Kitchen--presents a foil (hey!) for the prejudices and corruptions hidden behind the curtains of small-town England. With the added wrinkle of period (it takes place during WWII), Foyle's War is an ideal launch pad for the psychological and historical complications that make satisfying mysteries. Foyle is too old to fight, but is driven by a fierce desire to contribute to the war effort--a facet that gives the series a rich self-awareness. Of course, part of the attraction is that every episode is basically the same, but within that, the plotting and dialogue are shrewd, more intelligent, and more moral than any American equivalent. But the main appeal comes from the actors. Kitchen's style is stunningly minimal; he communicates volumes with the merest squint. That makes his rapport with the supporting cast, including the impossibly named Honeysuckle Weeks, all the more rewarding. It also means that when he busts out and castigates the bad guy, you really feel like cheering.
Also compulsively watchable is the far darker Wire in the Blood, in which Robson Green (a terrifically hammy actor who looks eerily like Bob Odenkirk from Mr. Show) stars as Tony Hill, a crazy criminal psychologist who specializes in profiling serial killers. Along with police inspector Carol Jordan (Hermione Norris), Tony solves impossible sex-crime cases while navigating the sexual tension that develops between him and Carol. Again, every episode is essentially the same, but again, that's the attraction. Despite the gruesome nature of the crimes the show features, there's something very soothing about the repetition--and the northern accents don't hurt.
The most American of the English TV shows I've become obsessed with is MI-5, which follows the intrigue of British intelligence officers in London. Heavily influenced by 24 and Alias, this show also features a riveting repetition--the dynamics between the attractive characters never really change, even when the ingenious plotting has you wondering who's on what side. Plus, like 24, MI-5 pays fetishistic attention to the details of its characters' jobs. Unlike the other shows mentioned, it's urban, and very technological.
And if you're really careful, you can watch two entire seasons in a single weekend.