Not my main style, but I've practiced it briefly... I enjoyed it a lot, it actually shares a lot of similarities with baji-quan
(the style I normally train in). Close distance fighting with short, powerful strikes. Its military origins clearly show. Like in many Chinese styles, the mechanics of power-generation are very subtle, and in this case power comes mostly from the ground. Basically, there has to be a strong (if often twisted) line going from one of your feet up to the tip of your fist, so that the power with which you push the ground away with your leg is conveyed into your punch (which is pretty much the process going on when you push a car).
Not particularly pretty (with the exception of its imitative forms), but when done right, boy is it powerful! My instructor once demonstrated the mechanics of the basic xingyi-quan
stance by having our club's strongest guy, a 34-year-old weight-lifter, try to push against him. My instructor, who's a short 53 y.o. Chinese-Vietnamese, wouldn't budge... and then proceeded to effortlessly hurl my friend a few yards back with a sudden push.
It is one of my friends' forte, I'll ask him for advice on good reads regarding the style.