How about adding a balance-versus mode and achievements to the game? A Few Ideas

[ZorusX]

I really think that achievements should never have rewards or benefits. As soon as they do, they cease being a straight up achievement, they also become quests and rewards. You may as well just make achievements quests then.

Also this:

The main problem with achievements is seeking them out just to "catch 'em all" and not just getting excited and feeling rewarded when they happen to pop up for something you were already doing. For some people playing the game becomes about getting the cheevs and they lose a lot of the fun that way (and im entirely guilty of this on occasion).

I've seen this happen a lot. Grinding achievements should be avoided.

To be straight up though, I don't think an ARPG really needs achievements. In general it is a genre that doesn't really need it. The achievement is basically: Dont die. Kill things fast. Collect the best loot. Create an effective build.