The fire series are for AoE nuking, thunder series is for single target spike damage, blizzard is for oh-shi bind and heavy and run.

The past elemental wheel is clearly apparent, and sucks since so many mobs are earth-based and resist lightning.
Ex. Can kill a 53 Ixali with a thunder>thundara>thundaga combo, takes two of these combos to kill a 53 wolf. (and a 45s recast means that's not happening.

Hopefully that sheds some light, I feel very constrained with nuking.