I have one, have only autocrossed it once so far in completely stock condition (other than alignment) on stock tires. I previously had a 2006 DS/RTA WRX and had the opportunity last year to drive, at one event, the 2013 WRX that finished third at Nationals in RTA.
The gearing of the new car is about spot-on for most local events. It tops out just over 60 in second. It could be a liability at Nationals, however, where the more open courses may require rev-limiter bumps (always a scary thing in a stock-tuned turbo car) or a 2-3-2 shift every once in a while. My old WRX would do ~67 in third, as would the 20011-2014s. The flip-side is better power delivery than any previous stock WRX. Between the twin-scroll turbo and the shorter second gear, the car has much less lag out of slow corners.
I tried the car with and without torque vectoring (i.e. brake-based faux-limited-slip for the front axle) but haven't been able to draw any conclusions. I had my fastest scratch time with it off, but I did plow into a cone on the outside on one corner exit. Would I have missed the cone with it on? If so, would it have held me back elsewhere? Need more practice to say for sure.
It feels better in transition than the 2013 I drove thanks to the firmer suspension tuning. Because I haven't driven the new car on the same quality tires as were on the 2013, I can't draw any conclusions on sweeper grip. I will say that I haven't been able to get as much negative camber out at the front of the new car as was possible in the older car. I've only been able to get -1.5, others have been able to get as much as -1.8. The last generation cars seemed capable of as much as -2.5. So while the new car rolls less than the last generation thanks to the firmer springs and stock bars, it may not ultimately have any more front grip.
Compared to my old 2006, it's a massive improvement. Compared to the 2013, I think it's an incremental improvement. Mostly it's more precise. I think the good drivers will figure out how to exploit it's advantages over the last generation in due time. What I don't know is if it's enough better to challenge the Audi TT's.