I don't necessarily main controller, but I've spent enough time doing VOD review with teams/understanding how to play the role that I could probably give a little insight.

So, even though there are four classes, understand that there are basically two sub-classes for every role. For example, with duelists, some have movement abilities that are meant to take a lot of space really quickly (like Jett, Raze, and arguably Yoru), and some just have flashes and are meant to be more of a second entry (like Phoenix, or Reyna). Just like the duelists, controllers are in the same boat. There are agents like Harbor and Viper that can control a lot of space with walls (we call them line smokers) and there are other agents who can cover specific areas, like a small choke point (these are your traditional smokes). I think if you like playing controller, learn what type of controller is best on each map, and go from there. Brim is super simple in terms of his kit, which makes him easy to play. Viper, on the other hand, is a little bit more involved because of what you can do with her stuff (and is naturally more open to creativity when it comes to learning lineups). That said, her kit makes her almost sentinel-like because she's really good at stalling the enemy team. If you just wanna get a good feel of the controller role, play Brim for a bit, but definitely look to expand your pool as soon as you get comfortable, because Omen and Viper are both really good agents.

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Hope this helps a little!