Head gasket issues have been most likely resolved from earlier generations. As an example, this version of the 2.5i has improved the cooling circuit in the heads. There is critical routine maintenance, including keeping up with oil changes and changing the timing belt as scheduled, that will impact longevity. There is not a lot of data on the 2,5i. However, the CVT has been down scaled and lightened up for the newer Impreza and possibly even the newer Legacy. In Japan, they have taken the CVT and mated it with a 2.0 DI turbo charged engine, putting out close to 300HP. This would seem to be good news that the 2010-2012+ CVT has got some beef to it. What's not clear is the CVT fluid maintenance cycle. There is info for harsh conditions and towing, but it's weak on normal driving.
Recommend oil changes be done less than 5K miles with a 2.5i. Over that, the gas mileage decreases and idles rough.
Bottom line, it would be good to understand how a previous owner maintained the car.