Elemental Weaknesses / Affinity
[SIZE="6"]Make them matter.[/SIZE]
Why does a wind elemental take damage from Aero when it should absorb? The elemental system has always been very important in the series, it needs to matter again. It's part of the depth magic users have come to love and expect, and makes battles that much more interesting.
Along with a refactor to the way base stats work, make skills, spells and enemy weaknesses more potent, because at present they have an effect if any.
This is a change with no real downside, it's something hardcore players expect, and others will not be bothered by. It's something that really ought to be done, and a necessary part of bringing the game up to the expectations of fans. And all just some number tweaking.