What makes it unreliable? I don't know. Maybeeeee:

-In the bottom 4 of Consumer Reports car companies in repairs per 100
-In the bottom 3 in the recent German driver's satisfaction survey
-Tons of problems ranging from minor electrical things to windows falling out.
-And much more

It seems like its a hit or miss thing. Some people are very happy and swear by their VW's, others have been put through hell with their cars. My neighbour who is a VW/Audi tech (and now an ex. VW fan) has told me numerous stories from his dealership and many other people have complained about VW.

Chances are you won't be able to find a reputable company (JD Power, AJAC, Consumers Reports, etc.) that ranks VW above average, let alone near Honda/Toyota.