A new low in 'carrot & stick' progression design; in closing-off any kind of content to give the illusion there's more of it by unlocking. A new low in nickle and diming microtransactions.
Blizzard are already monetizing skins and sprays but now they are fucking monetizing speech lines?! Obnoxious. And before you say that it doesn't affect gameplay so it's good - it does effect the writing, the characterization and basically the heart of the game. In Multiplayer games, any piece of writing is crucial to set-up the characters, to give them personality and to give them voice, figuratively and literally.
Imagine TF2 releasing with only one line per class. Imagine if you had to unlock the rest line by line, trying to glue back together a character who was shredded in sake of 'progression' and microtransactions. Imagine any other game or any other medium with lines of dialogs stripped out of it and locked away until some asinine demand is met.
And how do you unlock speech back to the game? As i understand it, you either get lucky with the loot box and it has a speech line or you get lucky and the loot box and it has in-game credits that you can spend on buying the lines. (not sure if there's any other way to get credits). No one would be shocked if they add the option to buy it also using real money.
There you have it. At best this is a new low in bullshit game design where more and more basic properties of a game are put on an unlock treadmill to give fake and artificial sense of progress (fucking lines!), to act as a cheap tactic to retain players' engagement instead of having confidence in the actual game and to mask what might be perceived as too-little content in the game.
At worst, you have all that + malevolent intent to hollow-out the game in order to drive microtransactions.
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EDIT: I've been notified that Overwatch isn't the first AAA game to have locked speech content behind unlock system\microtransactions so i take back the statement of Overwatch marking a 'new' low. I remain disappointed Blizzard resorted to the same means and help to 'legitimize' this treatment of this content type since for me there's a value distinction between visual cosmetics and lines of character voice work.