The Warmage is the job advancement from the Magician's Battle Mage class, which is a destructive PvE class, As a Warmage, players will surely see their strength in PvE increase, and perhaps even PvP overtime.
The early stage of the Warmage may seem disappointing, and players will realize they still heavily rely on their Blizzard and Fire Emblem/Ball Lightning from their previous class, but this is the similar case with other classes. Warmages are undoubtedly still one of the strongest and highly demanded characters for MMs (Mission Maps) at this time, and with skills such as Backdraft and Snow Blues, Warmages will remain in demand.
You may consider of getting Backdraft first, or Snow Blues first, but both of the trees are extremely powerful and unique. The Snow Blues tree offers Disease, which is a super annoying AoE, capping enemy's maximum HP and MP to a small, small amount. While you also get Fire Ink! that harshly drops their aim.
Backdraft tree offers more and more active skills but most of them are penetrate-skills that has the duration of 1 second, not like Ball Lightning, these skills fly really fast and only works when mobs are queuing in front of the caster.