Dont forget he introduced a very strong Education system where he raised the literacy level of his territories to about a 90 something% which would be very impressive for that time. Moreso his Agricultural reforms were outstanding, the people of Wei would never starve and his armies where always supplied. He was able to raise an army larger than Wu and Shu's combined.
I personally think his best success was with incorporating the "Barbarian" people into his own empire and into his Armies. His Wuhuan Army was a fearsome, well known, army that was once a part of the Yellow Turbans. It must take real skill to get an oppressed people into calming down, let alone joining your army...