Hi!
So, you have the hardcore-players. Forget about them for a second.
Think of those guys people often refer to as casual gamers for a second. They like TitanQuest. They play it a lot. They die a lot when they encounter the bosses of the game.
And do you know what the problem is, here? It is totally frustrating to nicely cut through waves and waves of cannon-fodder only to die 30 times in a row at cerberus or whereever.
And do you know what's even more frustrating? When the casual player finds out, accidently and weeks later, that he should have worn this or that equipment for this particular resistance which would have been brilliant against this particular boss.
Here's a question: wouldn't it be a nice gesture to let the player actual KNOW what to wear againt which boss?
I admit, that sometimes the player can guess after dying once or twice: Cerberus looks like he's dealing poison (and pierce i guess). Alright. So, what about Charon? What is his damage? Water?? What about Hades?? The effects are so vague (even if they look cool, which many do) that you just CAN'T tell even after dying 10 times. And there is no chance to "observe" your boss either: when he instant-kills you in one second with an unknown type of dmg, you just cant tell.
So, my suggestion is: give a visual hint about what the boss prefers as main damage BEFORE the player actually encounters him, so he can go shopping or change his equipment tactically.
This would make the player feel a) clever, b) in control, c) full of love for the game and not frustrated because he keeps dying without even knowing what hit him...
For example, in the room before cerberus there could be some misty pool with green slime. Everybody would know: "uh oh - poison coming right at me!!". Or the lyche-dragon with all the skeleton suggests life-leech or vitality damage... but he casts stun-wings and ice... wt???
The big yarren (sorry forgot the name... he's somewhere through a cave at the silk-road) does an ok job. What kills is the mixture of stun and blizzard: freeze and blizzard would be better as the whole area is icey. And also, the blizzard is physical dmg at the most part. But the direction is generally good...

In the obsidian halls there are those magma-eruption and inbetween the sepulchre-wyrms. That makes sense to me: as a player i see the fire and think: "ah, i should check my fire resistance". The same goes for the bull at the yellow castle/emperor (also the player only knows when he sees the bull, not beforehand)
I understand that the bosses have more than one dmg. But i suggest you take the most deadly one, or the general direction (elemental, or draining or poison or whatever) and mark that.
Just a thought.
PS if you DID give hints and i am just too thick to see them, you are free to point fingers and laugh at me.
