https://www.gamespot.com/articles/grand-theft-auto-4s-open-world-is-still-excellent-/1100-6458753/

In 2008, Grand Theft Auto IV came at a time when open-world games were a dime a dozen. With the open-world framework set by GTA III, where player agency inside a large and expansive setting is given all the focus, Rockstar Games' big return to the criminal underworld of Liberty City had to overcome some high expectations and other competitors that advanced the genre even further. Though GTA IV found remarkable critical and commercial success, many fans found the game's more grounded and subdued tone to be somewhat jarring, especially compared to GTA San Andreas' outlandish, over-the-top campaign.

When you look at GTA IV in the broader sense, it was more interested in immersing players into the atmosphere of Liberty City. With a larger cast of characters, along with several new systems to learn while exploring a more dense city, the new setting offered the most dynamic space in a GTA game at the time. And now celebrating its tenth anniversary in 2018, we're taking a look back at Rockstar's seminal sequel and how its more realistic take and focus on immersing players into its dense city opened doors for many other open-world games thereafter--setting the stage for Rockstar's biggest success, GTA V.