Monsters are generally pretty stupid in their tactics when attacking and defending.  In particular, changes I can see:

  * If monsters have defensive spells/devices, should use them at the start of combat.
  * If monster has healing devices, should use them when wounded beyond some level.
  * Monsters can too easily get stuck behind walls - they should be better at finding a path to the player.
  * Monsters should choose their attacks more intelligently - maybe let them 'cheat' in that they can know what attacks to avoid against players.
  * Monstrers should not stand around near the exit they last saw a player exit at (kills others entering map right away sometimes), but shouldn't walk away right away (to avoid issues of players entering and leaving a map rapidly and attacking with ranged attacks). 
    * Perhaps base partially on if the monster has fully recovered hp from last being attacked or not.