Some kind of tooltip would be helpful for deciding on item upgrades or passive points would be helpful.
Such as if you hover over an item or passive it will show you what stats are increased or decreased and how it would effect average damage, crit, etc.

It feels very unintuitive at times on what items would be better then others. I often find myself looking at the character sheet while equiping/unequiping items to see how those items will affect my stats.