well hell, i wont be able to implement these ideas anyways

so i might just give them to you ^^ well for starters, an ability customization system would be exceptionally good, each hero should have a choice on what abilities to actually take and what effects they would have, and they would use a certain currency for doing it.
Items enhancing certain effects of each ability should be taken into consideration too (or adding an effect to one)
those abilities should be able to get upgraded, for example a shadow bolt early game should become a shadow storm later on.
also, i never had the chance to make a good looking UI for these ideas i wanted to implement, sort of a "talent tree" but i'm sure you'll figure it out (its kinda lame to buy abilities from a shop screen, dont do it)