The game interface is fully customizable, although the classic Sierra interface is supported by default. You need no programming experience to make a game using AGS - setting most game options is just a matter of point-and-click (though scripting is of course available if you prefer). AGS manages most of the game so that you don't have to - it provides load/save game functions, inventory management, and more.

Add in some interactions (ie. what happens when the player clicks on various things) and you're done. You can even create a standalone EXE file containing your entire game, which you can then distribute.

So, how much does it cost? Nothing. That's right, AGS is free, and you can even create commercial games with it (subject to license terms).