We bought one of these for my wife about 3 years back. It gets great economy but not at the expense of performance.
It runs a 2.0L turbo diesel motor that makes 138HP and 236ft pound of torque. The trick is that it makes it all by about 2500RPM. Combine that with the 6 speed DSG sequential box and it gets up and goes. I test drove it back to back with the regular 2.0 petrol Jetta and it spanked the petrol engine version. Turbo lag off the mark is noticeable but once it gets on boost it really hauls. The traction control regularly kicks in off the mark. A re-flash of the ECU will add 25HP and 30 ft pound of torque with no real negative impact on economy.
It's very civilized to drive and the only time you can even guess it's a diesel is at idle. Once it's going you hear very little diesel engine noise.
It gets about 600 miles to the tank on a long trip but even driving to work and round the city it still get 500 miles from a tank. It's not even a particularly big tank at 55Litres (14.5Gal).
We are very happy with it.
Cheers