The drive-train is essentially unchanged from the '08 STI I had. That's good, because the issues that were known then have been ironed-out (eg, ring land failure,) but that also means your efficiency will not have improved much, so expect very poor mileage from such a small car - i drove moderately (granny around town and on the highway, with Max boost on on-ramps or when safe to accelerate that way, such as during my morning commute, being the only one on the road) and averaged 21 mpg over 60k miles. I could not get more than 26 mpg all-highway.
I would have kept the car forever had it not sustained $19k in damage a couple of years ago when some lady turned left out of her complex right into me...
I've driven big, powerful N/A cars (short-term) and loved it, but, with the STI, conditions can be set for an intoxicating, violent onset of boost that I'd not experienced anywhere else. A safe way to experience this (and to get a satisfying Yelp out of you passengers) is to shift early into 2nd gear and mash the go pedal. Max boost will come on quickly, just before 3k RPM, and the car will LAUNCH forward.
Be careful, because redline just before 60 mph will come before you know it and you'll look like a fool if you're not prepared. I typically let off of the gas and clutched-in for a relatively smooth transition to a coast past 60 mph and would shift to 4th or 6th, depending on the circumstances and speed limit.
If you couldn't tell, I miss my STI...
I chose the Forester XT as a more practical replacement with the baby on the way, and while it's great, it's not an STI.