Play Rogue if you want more Black Flag. Play Rogue if you want to learn about the complex relationship between the Assassins and Templars. Play Rogue if you hated Unity and want a better Assassin's Creed experience this year.
Those are the three cases I can think of where you might end up playing this game. Is it essential? Absolutely not. But there's a decent game here, and my only real regret is you can tell there's the potential for a much better game if only the developers were given more to work with.
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