The Impreza has a gutless engine that is tuned for fuel economy. The problem is that to get any real performance, you sacrifice fuel economy, and still dont get very good results. After the first two tanks of regular unleaded, I have resigned to the fact of only using 98 unleaded to get some power.
My specific Impreza has been plagued by interiors problems, with it it going back to service department 5 times in the first 3 months. These varied from rattles throughout the car, to the dash physically coming apart. I have given up on trying to get some of the problems fixed. Disappointing considering quality is one of the reasons you justify Subaru's more expensive price over it's competitors.
On the practical front, the Impreza is hard to beat: the back seats fold completely flat, and while the boot may not be as big as the competition, it is definitely much more useable. I have used it for my bike (both wheels still attached), surfboard, camping gear. The six speed manual is great on the freeway for creating a quiet environment. The AWD does make a huge difference in the wet, and the car has the stability of car that is at least once size larger.
Overall I am indifferent with the car. I bought a Subaru after owning a Mazda 6; I made the assumption that the change would result in a similar quality and driving experience. How wrong I was!