When you watch Stephen Zimmerman, you're not overly wowed by any one thing he does. Though he's athletic, he won't block shots above the box, or dunk all over anyone. Though he's big, he's not thick like Jahlil Okafor or long like Anthony Davis. Though he's skilled, he doesn't shoot like Dirk.
It's because he's smooth. Polished.
Because even though there's not anything Zimmerman does that's flashy, he makes the game look easy. When he turns in the post for his left hook, it's a simple motion. When he faces up for a jumper, the release looks clean. When he grabs a defensive rebound, you're not surprised to watch him lead the break.
Put all of that together, and you get a 'wow' player, even if no one thing he does wows you.