The reason Cabernet Sauvignon is so popular of course is that at its traditional best, in the most famous vineyards of Bordeaux, it can be so very, very good. In fact, contrary to popular belief, Cabernet Sauvignon is not the most planted grape in Bordeaux; Merlot is by a long way. This is because Cabernet ripens so much later than Merlot and can be very difficult to ripen fully. When it fails to reach full ripeness it can smell particularly green and leafy and it tastes a bit lean, tough and hollow. It is to fill this hole in the middle of the palate that so many Cabernet wines contain a certain amount of plumper Merlot.
The most classic Cabernet Sauvignon is one from a seriously run château in the Bordeaux regions of Medoc or Pessac-Leognan sub-district of Graves. Here, the soils are particularly well drained so that the vines dry out fast after rain, are encouraged to develop deep root systems, and tend to ripen the grapes quite effectively. Such wines (which usually contain some Merlot, a little of Cabernet Sauvignon's more aromatic relative Cabernet Franc and occasionally some Petit Verdot) demonstrate all of Cabernet's noblest hallmarks: exceptionally deep colour that is bluish purple when young (thanks to the grapes' thick skins); in young wines a particularly high level of tannins, the preservative that dries out the insides of our cheeks (due to the same phenomenon) and therefore an almost unequalled capacity to age in bottle; and a special affinity for oak, the vibrant signature cassis/blackcurrant fruit melding particularly well with the cedarwood and cigarbox aromas of new, top-quality French oak. Even today, when the grapes for such wines are being picked later and later, Bordeaux Cabernets tend to taste quite dry (as opposed to sweet) and can be inky and austere even until seven or eight years old. But underpinning all that structure (in a good example) is an extraordinary intensity of subtly layered fruit that can take 20 years to develop into a bouquet of haunting interest.
To my mind, the only other wine region that can claim to make Cabernet Sauvignon of a similar level of quality and in quite considerable quantity is California, specifically the Napa Valley (although Sonoma and Santa Cruz Mountain vineyards have also established admirable track records). These Cabernets have a similar intensity and, sometimes, flavour to the Bordeaux greats - they may even be equally tannic - but they tend to be distinctly riper, a bit more alcoholic, and sweeter. And few have (yet) proved that they can improve over decades rather than years.
Also in the United States, Washington state has been developing a reputation for dependable, user-friendly Cabernet, but here the wines tend to be less intense, more open and have a quality I can best describe as very bright, sharply etched fruit marked more by good natural acidity than inky tannins. I've had the odd Texas Cabernet like this too.
Chilean Cabernets are quite different. (They also tend to be differently priced, although a few would-be Napa-like bottlings are emerging from South America.) The cuttings for these Cabernet vineyards were imported from Bordeaux more than 150 years ago but have since adapted themselves to Chilean conditions. They tend to produce much softer, gentler, fruitier wines that can be enjoyed when only a year or two old and often have a vague whiff of milk chocolate about them, followed up by something ever so slightly salty on the palate. Argentine Cabernet is a relative rarity but is more explosive in flavour and more velvety in texture.
South African Cabernet is, as they say in France, en pleine évolution. Only very recently one could characterise it as being particularly tough and tart (for local wine lovers had been taught to admire tannin above all else and vine growers tended to pick conservatively early). But this is changing rapidly and there are some fine, still blackcurranty, often slightly floral Cabernets made both for early and medium-term drinking. Some of the fruitiest (and most unusual) Cabernet I have ever tasted came from Robertson - and was all the better for never having seen oak.
Australian Cabernet Sauvignon is some of the most distinctive (although obviously as elsewhere it can vary enormously in quality, from what is basically just red wine to something extremely ambitious). There is often more than a hint of eucalyptus on the nose of these dense, 'thick', full bodied wines, and the Cabernets from Coonawarra, supposedly Australia's perfect spot for Cabernet (although I would nominate Margaret River in Western Australia) can be quite tough and mineral-flavoured. Barossa and Southern Vales Cabernets tend to be much sweeter - particularly when they are blended with Shiraz, which they often are. New Zealand versions, produced in a significantly cooler climate, are lighter, high in acidity and, often, leafiness, although they are getting riper and toastier.
Cabernet is grown all over Europe, in very different conditions. In eastern Europe it rarely gets the oak treatment it deserves. Germany and England haven't a hope of ripening it on a regular basis (it's difficult enough in Bordeaux). The Loire Valley is growing more and more of it, though it is always lighter and gentler than red bordeaux and can be difficult to distinguish from the more widely planted Cabernet Franc. The Languedoc has yet to provide any stunning Cabernet.
Spanish wine producers have tended to swamp it with sweet, vanillin American oak, which does Cabernet no favours. All too often, early vintages of young Cabernet vines imported into a new country are just too simple, like alcoholic blackcurrant juice. Most producers learn that Cabernet is usually happiest when oaked and when blended with a fruitier grape such as Merlot, Syrah in Provence or, in the case of Austria, Zweigelt. Tuscan wine producers have long been trying to get the proportions of their manifold Cabernet/Sangiovese blends just right, and many of them, led by Sassicaia, have shown that Tuscany is probably the most likely third candidate for Cabernet paradise on earth, after Bordeaux and California. Tuscan Cabernet tends to be marked by firm structure, a certain but not unattractive bitterness, and a distinctly savoury flavour.
But perhaps the most distinctive Cabernet of all is that produced by Château Musar in the Lebanon. Here it is blended with Cinsaut to produce a unique, long-living cough syrup of a wine with enough wily charm to confound all but the most prejudiced wine drinkers.