Unlike earlier GTA games, it takes a much more serious tone with an emphasis on realism. They tried to get the physics as realistic as they could, there are a lot of subtle details in the world which adds to the believability, and NPCs react to you and your actions in some very interesting ways. The story missions are much more subdued and slower-paced, more grounded than earlier games; and while characters still have their quirks, they are also more believably written. The story is good, and the missions are good, but the game drags on too long. The pacing is just too slow. Going out to do activities with the characters was a nice idea, but it didn't work out. It quickly becomes busywork, and having people call you up constantly to invite you out to places gets old very fast. Overall though, I've played few games that were quite as immersive as this one. That's definitely the game's strength, alongside characterisation, which Rockstar really shines in with this installment.
Visually, it looks very gloomy and depressing without mods. On PC, you have the choice between a blurry mess (Definition: Off), a jagged aliased mess (Definition: On), or an ENB mod (if you have a supercomputer). The gloomy atmosphere fits with the gloomy story, but there's a weird contrast between the relatively serious gritty story and world, and the wacky radio stations, TV, and advertisements. Let's face it, there's also a dissonance between Niko as a sympathetic character, and the kind of violent chaos the player will probably get up to outside of the story missions when they get bored, but I'm not sure what the devs could have done about that, beyond writing him as a psychopath.
God, do I hate the way this game controls though. The Euphoria physics engine makes for some interesting unscripted moments, but it's so entrenched in every aspect of the gameplay that it ends up being a detriment. Your inputs are delayed by Niko's sluggish animations, there's no precision to your movement, or any action you perform, and sometimes he just wont do what I want him to do, particularly when it comes to moving in cover or climbing ladders. It doesn't really feel like I'm directly controlling him, it feels more like I'm giving him some vague instructions that he might disregard if he wants to. Niko takes forever to do fucking anything; and sometimes when I die, or fail an objective, I don't feel like it's my fault; I feel like it's the game's fault for not properly transferring my inputs with the controller to actions on the screen. It's one of the worst, most infuriating feelings a game can give me. An obsession with making everything look realistic had a severe negative impact on how intuitive the game feels to play. Driving isn't much better, controlling like in the words of Yahtzee: "shopping trolleys full of bricks". On the flip side, the vehicle deformation physics are still quite impressive ten years on.
I was down on this game for a long time, and I'm still quite down on it, but now I see its value... Sort of. It's not for everyone, and I'm glad they ended up toning down the super realistic angle for GTA V. It doesn't have anything close to the charm of Vice City or San Andreas, and while it's certainly more immersive, it just doesn't compare to the pure fun of those two. On the other hand, I'm glad I experienced this game, and it is very unique and unforgettable. I'll give it that.
The PC versions loses points for being one of the worst ports in history though, and time has not been kind to it. It still plays like shit on my 960M, and it's a nightmare to get running on Windows 10, particularly if you're using an Nvidia Optimus enabled laptop. Have a good, powerful desktop PC, check PCGamingWiki, and prepare to do some serious tweaking. It's such a ridiculously shitty port that I'm taking off two whole stars for this reason. If it wasn't for the quality of the port, I'd grant it 4 stars... Just about.