They have a knack for building cars that people want, are usually late to new developments, but then blow the competition out of the water in terms of sales, because their cars (prior to the infotainment debacles and cost-cutting measures of recent years) tend to be extremely polished, are comfortable, economical and handle very well. The Golf GTI in particular is perhaps the perfect embodiment of the company's capabilities.
Personally, I think some of their past clout, especially in regards to quality, has been overstated though. We've considered new VWs long before recent quality problems, but they left a worse impression than comparable French cars and in absolutely every way. Still, they have been very consistent for a long time and appealed to buyers with a "no experiments" kind of mindset, who just want a predictable rolling appliance.