So we have established that if you mostly drive faster than 70mph, do mainly short trips with a cold engine, or drive a lot in stop and go traffic, or if you think it is underpowered, and make up for it by hammering the crap out of it, you will not come close to the EPA MPG numbers.
However there are other drivers, as evidenced by the data on Fuelly, and the multiple posts here from owners, who are achieving the EPA numbers (driving both the CVT and the 5 speed). Nobody here is paid to lie about their mileage, good or bad.
Keep in mind that just because you don't achieve the EPA numbers due to your style of driving or the type of driving you do, it does not mean nobody is achieving the EPA numbers with the new Impreza. Don't believe me, look at the data yourself on Fuelly, which has far more MPG data than any other source has accumulated so far.
If you are thinking about buying the car, definately consider the experience of the high speed or short commute or bumper to bumper commuters to decide if it is right for you, or if you would be better off with a prius. Also don't buy it if you think it is underpowered compared to what you expect. That is dumb, and you will be disappointed. There are trade-offs in buying a non-turbo 2 liter AWD car that runs on regular unleaded.
Consumer Reports still recommends the car and has not said anything about the poor mileage -- actually they praised the mileage for the AWD Impreza, so keep that in mind. They also predict this car will be among the most reliable on the road. Those are facts you can check for yourself.
If you hate the car stop fretting, the resale value is high and you can get something else, there are plenty of cars to choose from. Don't let the forum door hit you in the butt on your way out.