From John Palmer's How to Brew, "Common Off-Flavors":
Acetaldehyde
A flavor of green apples or freshly cut pumpkin; it is an intermediate compound in the formation of alcohol. Some yeast strains produce more than others, but generally its presence indicates that the beer is too young and needs more time to condition.
Cidery
Cidery flavors can have several causes but are often the result of adding too much cane or corn sugar to a recipe. One component of a cidery flavor is acetaldehyde which has a green-apple character. It is a common fermentation byproduct and different yeasts will produce different levels of it depending on the recipe and temperature. Cidery flavors are encouraged by warmer than normal temperatures and can be decreased by lagering.
If it is caused by aceto bacteria, then there is nothing to be done about it. Keep the fruit flies away from the fermentor next time.
Estery / Fruity
Ales are supposed to be slightly fruity, and Belgian and German wheat beers are expected to have banana flavor components, but sometimes a beer comes along that could flag down a troop of monkeys. Esters are produced by the yeast and different yeast strains will produce different amounts and types. In general, higher fermentation temperatures produce more esters. Next batch, contrive to lower the fermentation temperature by a few degrees.
So my second guess would be that the fermentation temperatures got a little out of control.