Click Titans is almost a direct clone of Clicker Heroes, a web game where you buy heroes to kill enemies to make money to buy more heroes to kill more enemies to reset your game with more money in the next one (in order to kill more enemies). I like Clicker Heroes, but CT is just a way worse version. Mired with pop-ups for ads and opportunities to watch videos or pay in exchange for quicker game progression. Since the only point of "idle" game is the progression, it's a bit silly to expect people to pay for it.
At least there's a neat achievement system where you get some 'premium' currency by doing tasks like killing a billion enemies and things like that. I'm a fan of achievement systems that reward the player with actual in-game bonuses. It's also true that the premium currency is super easy to spend and that the bonuses are things that artificially improve your progression for a short while, so it's not really worth it. You can spend it for everything, resetting cooldowns, giving you gold, increasing your damage, things like that. The game will pester you constantly to watch videos in order to get diamonds, you can also pay for them, which detracts from the game.
The gameplay is restricted to tapping to deal damage and to buy heroes and activate skills to defeat a never-ending stream of monster in order to get goal to do the same thing, forever. The game has a nice art style and the feel whenever you tap is okay. Even with that in mind, this kind of game doesn't work well on iPads and phones. Clicker Hero and Cookie Clicker 'work' because on your computer you can easily multitask between whatever you're supposed to be doing and the game tab to click on a few things, but there is no such multitask properties to tablets and you won't spend an hour in bed tapping almost forever in order to buy the next level of a hero that will allow you to kill slightly bigger monsters.
Maybe you could pay real money to blast through enemies as fast as humanly possible, but you would literally be exchanging money for progress at a 1:1 ratio, which is crazy.