It has Levitate for an ability, so it basically has no weaknesses (unless its ability has been swapped/negated.)
You mean appart from a x2 weakness against Ground?
EDIT: Too slow. :< Anyway, I'd assume (haven't actually used one) that it would be quite good because it has quite a high BST. On the other hand, its best stat is attack, and it only learns two physical electric moves (Spark by prior evolution and Wild Charge by TM.) Additioanlly, you'll need an Thunderstone if you want to evolve it to Eelektross.