Even though he's kind of a tertiary character, Chouji has always held his own in battles. In the Chuunin exams, he took down one of the four sound ninjas. In the final battle of the anime, he grows to monstrous size to take on the giant...well....monster.
Chouji has a lot of potential inside of him. He has a surprisingly high amount of chakra, something that is possible in his family line because of their eating habits. He also has some really cool techniques, like the butterfly chakra wings above.
He can also grow parts of his body in size, or his entire body. It allows him to combat bigger, stronger opponents, plus it's just pretty cool.