2005's are deadly reliable and overall very well made cars. Same 2.5L driveline as all 05 Scoobs save for the six cylinder and WRX models.
Lighter than the OBW, and slightly better city mileage, but highway economy is about the same as the larger OBW due to the lack of difference in aerodynamic quality. Expect about 10-11L/100km in town and 8-9 on the highway.
The Impreza wagon is cheaper to insure and carries more stuff, though the cargo area is much smaller than the OBW.
One of the few "major" difference in the driveline between the base Impreza and the OBW is the Impreza was not available with a limited slip in the rear diff.