What makes Ash's Pikachu special is:
-He doesn't want to evolve.
-His thunderbots hit even ground-types. (Kanto and Johto only)
-Can tie with legendaries as well as lose to untrained pokemon.
-He didn't need to die and be born again as a Pichu to learn Volt Tackle.
-Yet he forgets his signature move for a mainstream Electro-ball.