In 2nd edition (May it Forever Rest In Peace) the Eldar codex was a thing of cheddary evilness and Swooping Hawks were one of the nastiest offenders.
These were models armed only with lasguns and the Swooping Hawk Grenade Launcher (SHGL). Before I describe how nasty the SHGL was, let me describe movement. In 2nd Ed, jump packer's moved 18 inches instead of the normal 5 inches for marines. Swooping Hawks, being Eldar, were much fast and could fly 36 inches in a straight line. In addition, you could fly over enemy models. When Swooping Hawks did this, they could choose to drop one krak or frag grenade each on one model they flew over. Imagine: you're a marine squad sneaking up with no enemy in sight and then suddenly 5+ krak grenades drop on your head. Ouch! Of course, you had to roll to hit and to wound and to save, but it was a nasty attack, especially since once the hawks landed they could shoot with their lasguns at another target!
On top of all that fun, they could assault and use their krak grenades against vehicles. Many a dreadnought's last vision was the colourful wings of attacking swooping hawks.
Ah, the good ole days. Third Edition changed all that. Swooping Hawks were gutted to the point of being next to useless and, except for the Exarch, lacking personality. The SHGL became a one time use weapon only good on Deep Striking and being inaccurrate as crap. Sure, the lasguns got upgraded to lasblasters, but with the saving modifier from 2nd Ed removed shooting at anything in power armour became an exercise in futility. More than any other unit in the Eldar range, the basic Swooping Hawk warrior got nerfed.
On the other hand, the Exarch got unbelievable weapons and close combat prowress. So, typically when people take Swooping Hawks it is only as an Exarch delivery system. (Yes, some people take them for fluffy reasons, myself amoung them. We are a sadistic lot)
Anyways, my point is thus: Swooping Hawks need a makeover for the 4th edition Eldar Codex. Bring back something to make them flavourful and decently effective in more situations than they are now, and reduce the ridiculous close combat Exarch to something more reasonable.