Tried out Tap Titans after hearing about it in this thread. Yeah... played a good bit of it, but I can't say I'm a fan.
Tap Titans goes all the way down the freemium rabbit hole. It discards all but a thin veneer of story and gameplay in favor of a pure feedback loop of numbers getting ever higher. As your numbers get higher, so do the "enemy" numbers. Luckily, you can increase your numbers by accumulating and then spending yet another number. These numbers all constantly increase at ever greater rates, but don't really ultimately mean anything. It's just--the "enemy" number has increased by a factor of ten, now you need to accumulate currency and increase your number by a factor of ten. This is made even more blatant by the way the numbers work--you go from K for thousands to M, B, and T, and then they just drop all pretense that the numbers mean anything and go to aa, bb, cc, etc. I mean, how many orders of magnitude even is that? It was around the cc mark that it really hit me just how much I was like a rat pushing a lever over and over (and over) again. This actually made me uncomfortably self-reflective about the whole idea of playing video games at all. And it was hard to stop!
But if the publisher can take advantage of my brain, so can I: I got frustrated enough when my main damage hero was killed to simply delete the app rather than waiting 10 hours for her to revive. And since I had already put in several hours, it pretty much guarantees that I won't ever want to start again because I would have to replay content. "Content," ha.
(Hilariously, the game can't even claim to be original: it's almost identical in structure to the browser game Clicker Heroes, even to the "Prestige" mechanic.)