West Ham signed Ward-Prowse on a four-year contract in August 2023 following Southampton's relegation from the Premier League.
And the England star has scored or created a goal in every match for his new club so far.
"He's a really good signing," said O'Hara on The Sports Bar.
The midfielder provided two assists in West Ham's 3-1 victory over Backa Topola in their Europa League opener and O'Hara was in awe of the midfielder's 'sensational' delivery.
Ex-Chelsea man Jason Cundy added: "It's also the consistency of his delivery - it's not just once, it's pretty much every ball, every free kick, isn't it?"
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But O'Hara's praise did not stop there.
"He's so much more than that as a player," he added. "He gets labelled as a set-piece specialist, but genuinely, he's got so much more to his game than people think."
And the former Tottenham star even admitted he wished his own club had managed to secure Ward-Prowse ahead of this season.
"I think he's fantastic, I really do. I wish Tottenham had signed him," said O'Hara.
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Tottenham have had a dream start to their season, winning four out of five games.
They sit second in the Premier League table just behind last season's treble winners, Manchester City.
Their next challenge will be against Arsenal at the north London derby on Sunday 24 September.
And O'Hara just wishes Ange Postecoglou was able to count Ward-Prowse among his players in what would surely be a huge boost for his squad.