A jacket's waterproof rating tells you how well its fabric will protect you from wet weather. Look for a higher waterproof rating (15K+) as well as fully taped seams if you spend lots of time riding through stormy weather or in a wet climate like the Pacific Northwest.
Heavily insulated jackets (down snowboard jackets or those with synthetic insulation weights of over 100g) are inherently warm and will require few layers underneath, while jackets with lighter insulation or none at all allow you the flexibility to layer in accordance with the weather.
Most snowboard jackets feature a powder skirt to keep snow out and a helmet-compatible hood. Beyond that, there are many options such as wrist gaiters, a variety of interior and exterior pockets, jacket-to-pant integration systems, and, of course, huge variation in fabrics and design.
It all comes down to personal preference and your own unique sense of style.
The ideal snowboard jacket keeps you warm when you're on the lift, dry when you encounter rain or wet snow, and breathes easily so you won't feel soggy under the shell.
In general, snowboard jackets tend to feature a more relaxed fit, a longer cut, and edgier style than ski jackets.