it's supposedly really powerful, but to me, it doesn't take away much hp and only hits 1/2 the time.
It has awesome power and always paralyzes when it hits but with 50% accuracy it's not recommended you teach it to your Pokemon unless they have mind reader or lock-on. A Pokemon like Magnezone or it's family for example could have zap cannon,lock-on and thunder wave(to prevent the foe from attacking you after you used lock on)
While it does have very high power and leaves its target paralyzed, 50% accuracy is very low, and not advisable to use. Conclusion: No, Zap Cannon is not a very good move.