Not interactive enough to keep my attention, and not idle enough just let it run in the background. In order to beat the levels, you must be engaged enough to do constant upgrades, but there's only one upgrade per tower. So it's simply watch money come in, hit upgrade button, repeat. Since it's supposed to be an idle game, there's no pause and the game just keeps on running even while you are surfing through the settings and upgrades. And there's a lot of menu options to dig through. It would probably be pretty fun if this were a true TD that used strategy to clear a specific course and/or upgrade towers based on your own style. But with only one path and one upgrade button (per tower) without any thought (or real goal), it's just monotonous and dull, and it comes across as just yet another vehicle for micro-transactions.