I love my impreza diesel. But I probably would find it hard to recommend to a friend or family member
The engines are known to die early on. Euro 4 and early euro 5 are the ones to look out for, my car is a euro 4 but luckily so far no hickups.
Remapping is a risk as the engines are known to be weak. I do want to remap mine but I am on the fence as don't want to kill my car prematurely.
I run a aftermarket cat back system off of a sti hatchback without a centre resonator, has a bit of a rumnle but still a bit tractor like, it's loud when doing a dpf regen though.
They are not particularly economical the best I've got on a trip to Wales was 49mpg on the computer but worked out 47mpg real world. Usually getting around 44mpg real world with mixed driving.
If it must be diesel and your after reliability and power your probably best of going vag route, my girlfriends vw 170hp tdi gets better mpg is faster than mine standard, much easier to drive around town has a wider powerband and can get 220hp with just a map