Hey Slaydon,i love ORPG maps,and i assure you that i have played the majority of them(at least those that deserved to be played).So i vote for ORPG!
Ideas:How about something medieval like you suggested?
It should be in countryside,with lots of grass and probably tones of strong and hostile creeps.You could design a terrain to match a war between 2 or even 3 races if you can...How about each race has 1 Big and Central town(with shops and other main stuff) and a couple of small outposts,just to keep the main town safe from hostile creeps/bandits.Now about the races,how about creating something classican like "Good" vs "Evil",this means a race which always served the good(something like High elves) and a race which is corrupted and only cares about destroying(you could use Scrourge or even a Demon race).The heroes should be some of all categories,i will give you ideas:Warrior(mass hp),Priest(damaging spells),Healer or Monk(Mass healing spells-low armor),Archer(damage dealer),Necromancer(Raises skeletons,disables enemies) and how about new something like a Buffer hero?Could be usefull.To make the game a bit more interesting you could make an Arena(players type -pvp and fight),where all players could fight between them or even better race duels,for example a fight between 3 heroes of the High Elves and Corrupted Demons.
If you like the idea,i could help you with some pretty awesome stuff to use in your map,like cool bows,fascinating spells,amazing swords,interesting hero models and much much more

~r3