Fire Emblem Heroes can be a game of rage until you get the Waifus and/or characters you want, after that you finally get to move on to the main story, your objective is to collect orbs, level heroes that you like, do pvp duels (Enemies are controlled by AI), Training tower to level your characters more, use SP to get new skills and get stronger and use orbs to upgrade your castle for more EXP, and more!
All in all I'd say it's an amazing game so far, but you really gotta reset until you get what you want.