Though you'll be pulled in a few directions at once, it won't take much prodding to get back to the main campaign. The narrative is exciting and exceptionally-written, and story missions, which have always been fodder between cutscenes, are now explosive set-piece moments amplified by the ability to swap characters. In one mission, you need to fly a helicopter above an office building as Trevor, rappel down the side of it as Michael, and provide sniper support as Franklin. It's thrilling, and provides an experience totally unlike anything you've played before--and it's hardly the best usage of this mechanic.
It also helps that just about every mechanic is a marked improvement over previous iterations. The most noticeable improvement comes with the visual overhaul that makes GTA 5 one of the best-looking games currently available on consoles. But this improved fidelity comes at a cost. The game's massive, sprawling, detailed San Andreas is obviously pushing the hardware to its limits, so don't be surprised to see framerate drops or objects popping into existence as you speed down a highway. Other changes have only positive impacts to the game--gunplay is extremely strong thanks to improvements to the aiming, and while the driving controls are looser than they are in some other open-world games, they make for some thrilling chases.
These mechanics come to a head in the game's heists, which take advantage of every improvement Rockstar has made to its franchise. You're not just showing up to a question mark on the map and taking part in a bank robbery mission, you're an integral part of the planning process of awe-inspiring cinematic moments. Being able to choose between two wildly different plans, deciding on the getaway car, picking from a handful of different teammates--you're in full control in a way no other game has ever attempted. When the mission actually begins, you're able to see your hard work unfold, with different outcomes depending on your planning and actions.
Rockstar also made sure to create an economy that actually makes sense, instead of just dumping money into your in-game bank account without any real purpose, as was the case in past games. You're able to customize every weapon and vehicle in the game, and there's a robust real estate system with dozens of different properties around San Andreas that can be purchased. Some feed more money to you, while others actually open up new tasks and missions. There's even a dynamic stock market that actually reacts to in-game events, letting you make even more money by researching missions before you complete them. The number of moving parts in GTA 5 is astounding, and you'll be amazed by how well they all work together.
Five years ago, it looked as though it would've been difficult to make a bigger, more impressive game than Grand Theft Auto IV, but Rockstar didn't just settle for improvements to visuals. Instead, it polished and iterated upon every single element of the game--and the genre. The world is massive and detailed, the gameplay is damn near perfect, and though there are some lackluster side missions, the actual story is filled with memorable personalities that feel more fully-realized than even the best of GTA's previous characters. It's a remarkable example of open-world gaming at it's finest, and while it doesn't reinvent the genre or do anything all that new, it does so much so well that it's hard to find flaws in Rockstar's massive blockbuster.