What I would like in Avernum 5 is the alchemy system back, and maybe even expanded. For example, instead of having the only potions you can make be plain vanilla heal/bless/cure/haste buffing potions, you could make, say, volatile potions that would have a similar effect to a fireball, or poisons and acids you could apply to weapons. On top of this, the crafted potions could increase in efficacity with your alchemy skills, making an alchemist-style character a valid build.