First check that you got an original one (check the number on the back on the case against Aspire webpage)... if you got the normal Nautilus (BDC - Bottom Dual Coil) it should produce decent vapor... if you got the Mini (BVC - Bottom Vertical Coil) it should produce A LOT of vapor (for a tank, of course)
Also, if you "mouth-to-lung" try a closer airflow... if you "lung-hit" try a wider airflow.