One of the biggest problem is making spells feel powerful and unique, and certain spells need spell effects.
For example, the Assassin can really use some Cleaver, Knife stabbing sounds.

Another thing is that we're mostly borrowing SC ability icons, which can only serve us to a certain extent. If anybody can help us create better looking icons, that would be great.

Finally, an issue we have is with heroes not being visibly different from the spawn minions. Mutant looks like zerglings, Warrior looks like Zealots, and Archer looks like Hydras.
We're also looking to put some indications both on the minimap and on the screen to visibly show which unit is the hero. It would also be good if hero summons, like the summoner's zerglings and the archer companions to have a different model than the minion spawns.