tl:dr Another Ahab looking for his white whale.  This game tries to be Clicker Heroes meets Tap Heroes... and fails at being fun.

This game bills itself as an idle game but makes you constantly upgrade abilities or else your heroes will die and be useless for a period of time.  It builds itself as an incremental game, but the only thing incremental about it is the costs, the abilities are linear.  It bills itself as a fantasy game, but the only fantasy is the dev's dreams of you paying him obscene amounts of cash in an attempt to find something resembling fun.  You won't.  Fun was not included in the design spec.

This game is all about currency... and not in a good way.  You have gems, artifact fragments, keys (and chests to use keys on)... and gold.

• Gold buys heroes (like Clicker Heroes) and abilities (like Tap Heroes), and is relatively easy to come by.
• Gems come from achievements (some of which aren't actually possible to finish)... or from paying real money.
• Keys come from resetting after level 125 (you get 1 more key)... or from paying gems (which costs real money).
• Chests come every 5 bosses, and require 1 or 3 keys to open.  You can tell what hero the chest is for, but you don't know if the item inside is a weapon (attack boost) or item (health boost).  Both of which are useless later in the game.
• Artifact fragments come from every 35th boss, I believe.  It's ridiculously low.

On top of that, your heroes have different abilities that function as yet another currency.

• Level (which controls damage)
• Health (which is required to keep them from  dying and starting a resurrection timer)
• And a variety of semi-unique skills that may or may not be useful to you.

And then theres your artifacts (which are yet another currency) that are the only real persistent bonus you get.  Not only must you create each artifact (which one you get is random), but then you have to level it.  Both of which consume increasing amounts of fragments... meaning you'll quickly be needing hundreds of fragments just to get one advance.  You'll be lucky to get 10 fragments in a run (which, even with speed hacking, will take hours).

Costs for everything except keys go up exponentially.  Which means even if you did sink real money into the game, the bang for your buck is essentially on a diminishing return.  Further, the boosts you buy don't scale.  Which means even if you bought the $100 "big package"... it would only help you on the first few hours of a play through.  By the time you get to late game, you won't get enough gold to buy a fraction of an ability, and keys only open chests which by late game will get you a few million health... when your character is rocking health in the 1x10^108.  Yeah, that's right... 98 digits too low to even matter.  But the real tragedy is the game punishes you, constantly.  Hero dies because you thought this was an idle game and you looked away for a few minutes?  Well... after running all night and buying a bunch of levels... expect a half hour res timer.  Finally saved up enough gold to unlock a tier level upgrade?  All that time you spent leveling your other heroes is now worthless... as the upgrade is so incredibly huge that you've jumped your dps by generally a order of 1,000.  On the plus side, you're going to shoot through bosses.  On the down side, you won't have enough gold to level up health on your toons... before they get to a boss that one shots them.  Now stare at the screen and rage while you wait for your half hour timers.

This game does everything wrong.  Everything.  And then expects you to pay real money to try and buy your way out from some of the hate.