Well, you could wait for the enhanced edition to come out (free for you since you own D:OS), which will include a harder difficulty and a great deal of rebalancing so you don't have to gimp yourself to get a challenge.
But if you're going to play this version anyway, I'd avoid the magic shields, crafting in general (maybe still craft and use potions if you want), charm, summons, and any cheesy tactics that feel like they're only effective because they're taking advantage of the AI.
