recommended path, get to the big +5 damage, then go straight for enchanting. some of the best stuff is not an artifact so making it into an artifact is invaluable.
if possible,
consider adding classes for unlock
T1;
complete game with all of alchemy tree unlocked = alchemist who has a bonus to potion crafting and a new potion centered tree.
complete game with mage tree filled = archemage with ranged magic damage and default 1 mana regen, but negative resists, reduced max health, and reduced health gains.
complete game with warrior tree = berserker/knight, increased health gain 10% bonus to armor and physical damage gains.
T2;
finish with archmage and knight = battlemage, increased health gains, passive tree with elemental damage nodes instead of phys damage nodes.
knight +alchemist = rogue, make poisons?.
alchemist + archemage = potion based magic with aoe?.
would you consider adding a new feature (if "enemydamage">"playerdefense" = "player 1 hit kills enemy")? it's just tedious to be building for high magic mana, and defense, but low normal damage and plinking things to death while not taking any damage.
also, putting the number of active allied units in green, and dead in red, above their picture just so we can stay up to date with precisely how the battle is going.
would it be possible to add something like hero's specialization, as in "you have used offensive abilities on this hero so now your hero has become inclined towards offense *+1 to offensive skills*" but have it be an automatic bonus from using offensive abilities 1000 times or something. further examples "you have used poison arrow a ridiculous amount so now your poison arrow gets +2", "you seem overly cautious from your use of 'defense' so you now get +2 to defense" etc.
also why is there an anti-magnetic effect on the targets. you will drift randomly until the crosshair is anywhere near a target, then it constantly tries to drift away from that target.
even this one :)