Some of this may already be implemented, just not available in the current beta.  The whirlwind spell, for example, could be useful in tactical combat.  Or teleport.

I used to play an MMORPG called Dofus.  I would just rip it off wholesale.  They have tons of fun tactical spells and abilities.  Lots of differentiation between character types, too.

I'd like to have more capability to push units around, freeze them, and alter the terrain to my advantage.

Traps would be nice, too.  Anything that can be combined with other spells and abilities.  For example, casting a volcano and pushing enemy units into it.  Or fire that spreads from tile to tile, like in Romance of the Three Kingdoms IV.  Or, if we can have rivers in tactical combat, freezing a river, forcing an enemy onto it, and then thawing the river with fire.  May be difficult to code the AI to take advantage of these types of abilities, but it would make multiplayer tactical battles insane.