What's the easiest way to distinguish traditional style from Wushu?

Actually, it's pretty easy. Traditional gong fu usually is performed in a straight line, whereby the practitioner just goes back and forth performing his moves. With some of the animal forms, and with some of the advanced forms (Lohan Chuan, Ying Chuan (eagle), and Tong Long Chuan (praying mantis) comes to mind, for example) there might be some small "branches" that the practitioner moves on or off of that proverbial straight line, but how far one goes all depends upon the practitioner. Technically, traditional gong fu can be performed on one line, and, in a small space.

Wu shu, on the other hand, tends to be more circular in its layout, and, "all over the place". Remember, just because the kicks are high and acrobatic, or the stances low and the sweeps frequent, doesn't mean it's wu shu. Some of the traditional forms are pretty low and nasty to perform, especially the animal forms.

There are a few other noticeable differences. The stances are lower in wushu, and the feet are kept further apart than what you would find in traditional stances. Traditional stances find the feet, in mah bu for example, a distance of two and a half foot lengths. Mah bu as exhibited in wushu forms would be much wider.

Also, arm extension during strikes is different. In traditional gong fu, the arm is not extended all the way; there will always be a slight bend at the elbow. In wushu, the arm is extended all the way during strikes.