Fairy Tail's strength is that the one to one battles only last a chapter or two, compare that to One Piece, Naruto, Bleach, etc. and that means in a chapter, a one to one fight will have a beginning, middle and conclusion with a definite victor where in a series like Naruto or Bleach, a fight can last multiple volumes without somebody actually winning the fight.
Erza and Lucy being naked half the time is just icing on the cake.
It helps that the characters and powers are extremely straightforward.