Here are 3 games that are must plays if you like GTA and are looking for something similar.
First things first: The obvious choice here is Read Dead Redemption, but since we're assuming you played that already, here are three games to play before GTA 6, that you might not have thought of:
Sleeping Dogs
Honestly, I like Sleeping Dogs better than a lot of GTA games: It features better combat, had slicker graphics at the time, features a more unique setting, and has a more grounded storyline. But let me start at the beginning: Sleeping Dogs is your basic organized crime Kung-Fu flick, except that it actually has a good storyline that will have you engaged. Also, while you technically are part of the crime world, you really are an undercover cop, so that gives Sleeping Dog an extra element of story-telling that many other crime games never had.
So, put a pin in that for the story being great. What really sets Sleeping Dogs apart, though, is the combat: This is full-fledged Tekken tossed into GTA. While Yakuza attempts something similar, the combat there is much more... floaty. Sleeping Dogs meanwhile, really feels choreographed and just good. You almost don't want to use a gun whenever it's available, because it just feels so much better to use the melee-combat.
Sleeping Dogs was remastered since its release, so it stands the test of time and is easily a must-play if you're into GTA.
Mafia 3
Mafia 3 kind of gets a bad rep for its dull world, but honestly... if you just stick to the main plot, you're gonna have a great time with the game. The story is meaningful, and deals with the racial issues of the 60s in a realistic manner, while the voice acting and cutscenes are on point. Plus, you actually get to play a black main character, which is rare in gaming, and something I'd like to see Rockstar do with Read Dead Redemption 3.
Also, if you're into the whole Mafia thing, there's more than just Mafia 3: Mafia 1 and Mafia 2 have been wonderfully remastered, and some say those games are all-time classics. I say those people aren't wrong. I wouldn't argue with anyone that says Mafia is the better and more mature GTA... so... that's saying a lot, right?
Saints Row the Third
If the silly side of GTA was what drew you to the games, and you're sad about GTA 6 reportedly pulling punches, then Saints Row is the easy choice: It's all about being over the top and as politically incorrect as possible. Seriously, if all the chaotic GTA energy was bundled into a spin-off, then this is it. Meanwhile, the game still has good gameplay, and a good enough (whacky) story to be more than just a chaos-trip.