Aiming with a stick (top-down)

I'm creating a sort of tower-defense game. View -- top-down. My turrets aren't moving, but they can be rotated on the Y-axis, so that a player could aim $$anonymous$$s shot. The game should be controlled with a Xbox controller, so my turrets are rotating with a stick. Here's the script I am using:

 transform.Rotate (0f, Input.GetAxis ("Horizontal"), 0f);

It kinda does the t$$anonymous$$ng that I need, but in a very slow and clumsy way. I have to wait till the tower rotates and it takes a lot of time. I'm sure there is a way to improve it. For example when I tilt my stick backwards, the turret should be rotated 180 degrees on the Y-axis. Here's a visualisation.

Could you please suggest how to improve my code ? Thanks.

PS

Geometry Wars is a good reference here, in terms of aiming.