I am not certain if anyone has made a distinction between different degrees of fly-by-wire technology.
Technically, any flight controls that don't include a mechanical linkage to hydraulics or control surfaces directly are fly-by-wire - they have electrical connections to the hydraulic servo valves.
Whether or not there are flight computers in the chain is a different matter altogether. Fly-by-wire can be done so that the position of the flight controllers affects the position of flight surfaces directly (blowdown limits notwithstanding), or so that flight controls send signals to flight computer, which determines what the pilot wants the airplane to do, and parses the pilot inputs into the most efficient way to achieve the desired results.
Flight computers can be used to augment stability, prevent the airplane from exceeding its designed flight envelope, prevent certain pilot errors from ending in a loss of control and crash, and in case of military aircraft, maximize the performance (such as flying right at the critical angle of attack to maximize the lift available from the wing), and manipulate control surfaces in a more complex way than is possible with just four traditional control axes (pitch, roll, yaw and throttle). Thrust vectoring is one example that is usually controlled by flight computers. Another example would be the system used in modern Airbus planes that enables full control over pitch, roll and yaw even in cases where flight control surfaces are partially disabled, such as manipulating the wing slats, flaps, spoilers and rudder to replicate the effect of a disabled aileron.
And yet another example from Airbus A320 - if you are near the stall speed and push the nose up, the airplane automatically increases throttle, as demonstrated by Bruce Dickinson. Similarly, the plane can not be banked over certain limit...
As a rule of thumb - any aircraft that only has a joystick is also fly-by-wire by definition. However, for a pilot, there's really little difference how the control inputs are relayed to control surface positions - if it's a direct position translation, it's largely the same whether it's done electrically, mechanically or hydraulically.
Planes that have computerized fly-by-wire systems don't necessarily offer a direct way for pilot to put, say, elevators to maximum pitch-up deflection - they'll likely read that pilot wants to pitch up as fast as possible, then depending on the plane type and speed, move the elevator until the airframe's g-loading reaches maximum allowed, or critical angle of attack is achieved, which will achieve what the pilot wants.
Another rule of thumb - dynamically stable airplanes can be controlled by direct pilot inputs due to their tendency to fly by themselves (which is essentially what stability is). Flight surfaces are used to deflect the airplane from the balanced flight position.
Dynamically unstable aircraft require either reflexes of a jedi, or for more practical solution, active stability control by flight computer, since there the control surfaces need to be used to keep the airplane in a normal flight attitude as it tends to not stay in it by itself.
So, you can basically just look at planes designed before and after F-16 to define if the fighter is stable or unstable.
Stable planes can use direct flight controls, although there are other benefits from fly-by-wire that might mean the airplane still has electrical control linkages and even a flight computer.
Unstable planes require filtered control inputs handled by a flight computer.
Thus, the distinction between different types of fly-by-wire is fairly important.
As far as I know, the F/A-18 is dynamically stable airplane and can be flown with direct control inputs, but in normal flight, there are electronic flight aids that help the pilots in flying, letting them pay more attention to the radar, weapon, and nav systems management. There are also limitations to what you can do with just the pure hydraulic control system. A testament to that is the so-called "Frankenplane" crash. The Frankenplane was a Finnish Air Force Hornet which was contructed by taking the aft part of a damaged mid-air crash survivor F-18C (single seater), and joining it with a CF-18B front fuselage (two-seater), making it an essentially unique plane individual with unique wirings and such.
As the plane was on a test flight for determining if all the flight controls and such worked correctly, the flight control system apparently suffered a malfunction and was required to switch back to direct hydraulic control. Unfortunately, the plane was at the moment performing a vertical turn at low speed, nose pointing upwards and losing airspeed rapidly. With the flight aids disabled, it entered an unrecoverable dive and crashed. Both pilots ejected and survived.
At least that's what I've managed to parse together about the reasons for said crash.
