A point with great cleave - if you have power attack and a good attack bonus, it can be just as useful as whirlwind against low level goons and medium goons. My epic rogue/barbarian tends to get *GREAT* use out of great cleave. He chrages into battle, power attacks for a gross amount and then whacks away until one of his foes doesn't drop (ie; has more than 80 hit points). Then he uses his expert tactician to finish off that enemy and continue cleaving against anyone else that might drop.
The use of great cleave is a factor of campaign style. If your DM only uses small numbers of powerful creatures, it is likely a wasted feat. If they use huge numbers of lower level monsters, it can be very powerful.
As for an EK, I think you can get superior effects from PA and GC when compared to a fireball spell in some situations. For instance, a high level EK with shapechange and other spells can get a huge reach and massive damage per attack, especially with PA, arcane strike and other magics factored into the equation. I wouldn't expect it to be too hard for an EK to generate 60 points of damage in a cleaving circle based upon a colossal creature's reach ...