The Super Hornet is based on the regular Hornet, but it is essentially totally new airplane. It is several feet longer & wider & more wing area. The air intakes are square instead of oval, the wing has a distinct "dog tooth" notch near the fold line, the Leading Edge Extensions (LEX) are one continuous curve instead of the "S" curve and the horizontal tail has a straight LE corner instead of rounded. The ventral speed brake between the rudders was deleted infavor of a small panel on each LEX. They put 3 external stores stations under each wing instead of 2.
Changes not critical to modelers include much more fuel capacity, more internal room for avionics, better engines, cockpit updates, etc. It can carry and use more modern ordnance than the regular hornets.