In the ancient era most wonders are pretty nice and it feels good building them. However, the Hanging Gardens feel a little weak given that they are just a plain wonder plus an artisans quarter. To make them a little bit more interesting, maybe they could give a strong food / population bonus, like instantly increasing the population of the city by 5.

Alternatively, it would add very interesting game mechanics to the game if the Hanging Gardens would add a significant influence bonus (like +10 or +20, or +2 per population in the city) since then the Hanging Gardens would people people expand and/or getting more wonders. Having an early wonder that gives influence would make these choices more interesting.