This is the talent build that I recommend and use almost every match:
This of course relies on you building his talents in way that boost the damage of Cleave (Q) and his basic attacks. Zeratul struggles in the beginning of matches but becomes a ghost-like juggernaut that takes people out in seconds by the end.
It’s almost like a playing in Rogue in World of Warcraft. His stealth lets you sneak in and out of combat so you can pick and choose your targets without them noticing you. Hit it and quit it, that’s what Zeratul does.