The 2.5 WRX is a fantastically smooth and torquey motor and in PPP form is almost as quick as an STi. Our 2.5 has done only 32,000 miles but has needed the front and rear struts, secondary air pump and one of the air system valves replacing, plus cambelt tensioner. Definitely most costly of the five Imprezas we have owned, but we love it! I understand that it's not a good idea to mod the 2.5 north of 400 BHP...
Oh, and I run it on Millers CFS 10W-60 competition oil and treat it to the occasional drink of Millers octane booster. Also, never hammer it until fully warmed - no engine/tarnsmission problems so far.