We stayed in the Kefalonia Palace in late June / early July and throughly enjoyed it. If you're after a relaxing holiday this is the place.
Our advice take a book for by the pool, hire a car to see this beautiful Island and head up to one of the bars overlooking the sea, either the one owned by the hotel or the one further up the hill where the beer is cheaper.
The only grumble would be the entertainment or lack of it but it was too hot in the hotel bar at night anyway.
All in all a fantastic place, a great pool, nice staff and nice holiday makers where I'm sure a lot of friendships were forged.