It is designed to be addictive. The game uses a time system that stops you from playing after a bit, so you have to wait for ages, so you don't get bored with it. This is to hide the fact that it is a bland game with little actual content behind it. It's just another stacker; I could label it a Bejeweled clone if not for the fact that it has even less to it. It does nothing new, and only really adds annoying mechanics that addict and frustrate, causing you to spend more on the IAPs to get past certain bits of the game, because the entire premise o this game, like any low-quality King game, is to make a crappy ripoff of a good PopCap game (usually Bejeweled, but they've stolen Peggle as well) that is designed to siphon money from unsuspecting casuals like the evil fuel pump from the Michelin adverts.
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Candy Crush Saga is a game and all such electronic games are addictive so it too is. The whole premise of these activities is to get people hooked so they can not stop playing and so they keep wanting to put money into the game in order to become winners.
How the hell is this game addicting?! I tried to play it and after a minute and a half I put it down because I thought, "It's a f*cking stacker. Whats so special about it?" You try and match up stuff to other stuff. It's so ridiculous. I highly recommend to NOT buy this game. At all.