I know that the weakness of acid rain has been brought up before. Its a spell that is the same level as firewall, but has pathetic damage and duration. I thought I would start this thread on it however, because I just realized something about the spell that is very odd. It doesn't work like you think it would. Instead of applying an aoe damage tick every 2 seconds to anything within the rain cloud it seems to just inflict an acid dot on anything that passes through it. What that means is that something can go into the acid rain spell for 2 seconds, take damage, leave and continue taking damage for the duration of the spell.
This isn't acid arrow or burning blood, is this really how the spell is suppose to work? I can't imagine it is because the duration seems to be messed up too. Instead of making the storm last longer, which is what the tool tip seems to indicate it will do, the storm always seems to last a very short time and the spell just seems to add time to the acid dot. I don't think acid rain is suppose to be and aoe melf's acid arrow. It seems to me the spell should work more like acid fog, where enemies take damage as while they are in the area of effect. I may be wrong, and this dot mechanic could explain why acid rain doesn't have nearly the damage potential of wall of fire.
Many people have stated that casters need an acid or lightning alternative to wall of fire for those who take the lightning acid enhancements. It seems to me if you changed acid rain to function more intuitively like acid fog does, and added a +1 per level damage as well as lengthened the duration to +6 seconds per 3 levels instead of plus 2 you would have a very comparable spell to wall of fire. They're both level 4 spells, damage would be almost identical, 2d6+20 vs 3d4+20 and both would last about a min at max duration and extended. Acid rain would benefit from few mobs being resistant to acid damage, but wouldn't have wall of fire's bonus to undead. Overall it seems like a balanced solution. I just thought I would put this out here again, as I'm sure strengthening the acid line of spells is something brought up a lot, but most importantly could any devs confirm that an aoe dot is really how acid rain is suppose to work?