This is a great chest exercise for hypertrophy if you have good motor control. Start with the incline bench set at about 45 degrees, higher than you would normally use for incline bench presses or flyes.
With a slight bend in the elbows, initiate the movement by contracting your pecs. Really try to "open up" the chest.
Don't bring the dumbbells straight down; that will just hit your shoulders. Notice the natural arcing motion of the arms. The dumbbells start at the sides and should stop above the upper chest.
If you want to build huge muscles, you must continually challenge them by placing a greater demand upon them. If you stick with the same stress level month after month, you'll quickly reach a point where your body is used to the stress and won't need to adapt (i.e. grow) anymore.