Maybe something more general first, I prefer to see less enemies at once, really beeing attacked by a whole horde of Orcs, are you a mage or warrior, is quite odd. You should never be able to defend from that. You better be carefull and don't flee from one combat into another.
That said, spells should overall be more powerfull, but more consuming in time/mana. A meteor strike should either instant kill, or leave the target stunned, knocked down. Giving the mage a chance to finish him off. With melee combat or maybe a less powerfull spell. There should be a reasonable mana regeneration for this to work. Also to make it little more challenging, some spells would not be able to perform while moving, casting an powerfull meteorstrike wouldn't but a firebolt would. Having the mage to use the right skills in the right time. use a firebolt to lure a distant enemy, charge a meteorstrike and hit the target. If you lure more targets you better start running and keep using the firebolt spell. Aside from how combat is controlled.