The ability to crawl is a good idea, not to mention actually forcing you to use it also. Spaces where you can crawl through. Maybe to get to secret rooms, or just to advance on the level.
Eight-way shooting. Several frames for the jumping animation, not one animation for upwards jumping, freeze in air and landing animation. Have the character animated all the way.
Rolling. Running and shooting. Moving/runnig backwards/forwards while shooting in one of the opposite directions.