A new video game went on sale this past weekend. It was quite a thing.

The Western-themed Red Dead Redemption 2 quickly achieved a milestone: it racked up the biggest opening weekend of any entertainment product (including films) in history, taking in $US725 million in three days, according to its developer, Rockstar Games.

This put it second only to Grand Theft Auto V, another title by Rockstar, which took in more than $US1 billion in three days in 2013 but was released on a Tuesday.

By contrast, the highest-grossing film ever made, Avatar, made about $US240 million in its first five days of its release in 2009.

While it's important to point out that games like RDR2 sell for a fair bit more than a movie ticket, the news speaks to the massive interest in the title, which has garnered strong reviews, and the technical advancement in gaming it represents.

Give us the inside run on RDR2

Red Dead Redemption 2 is set in 1899, in the final days of the Wild West.

Outlaws still roam parts of yet-to-be-tamed America, among them Dutch Van Der Linde and his gang, who after a ferry heist goes wrong are forced to hide out from law enforcement.

Looting and killing goes with the territory in Red Dead Redemption 2. (Rockstar Games)

The player controls Arthur Morgan, one of the gang members, and follows him as the weather worsens, the gang unravels and loyalties are questioned. Players ride horses, loot, kill, hunt for food and just generally try to survive an unforgiving reality.

The game is a prequel to Red Dead Redemption, which was one of the most expensive games ever made at the time of its 2010 release and is equally praised.

"This is more than just a cowboy game, for sure," Rad Yeo, one of the hosts of gaming show Spawn Point on ABC Me, told triple j Breakfast.

"This is one of the biggest open-world games out there."

An open-world game? That's basically a game that allows the player a fair amount of freedom when it comes to what they get up to.

Rather than being locked into a linear structure, the player can roam and go off-script, often in a landscape that is large enough to explore for a long time (and by all accounts, the landscape of RDR2 is big).

There are several reasons this game is blowing up

One is attention to detail.

The open-world format allows for a level of engagement beyond the roughly 60 hours of plot and 500,000 lines of dialogue, as ING critic Luke Reilly wrote:

"I've sat and watched lumberjacks felling trees at a bustling logging camp and curiously tailed a perturbed Englishman wandering around town looking for his mate 'Gav'. None of this is crucial to the progression of Arthur's story; it just helps build a world around him that made me feel like a visitor rather than the centre of the universe."

Players need to bathe and eat, often by hunting for wild animals like deer, or fishing.

"It's so lifelike that even your hair grows and you have to trim it," Yeo said.

The horses fart, and the wild animals you hunt for food must be properly dealt with, lest they start to smell and attract unwanted attention.

Speaking of horses, there are a lot of them:

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Then there is the quality of the visuals, which Game Informer's Matt Bertz called "remarkable".

"The wide expanses of wilderness feel alive thanks to an unrivaled dynamic weather system, ambient sound effects, and the most ambitious ecology of flora and fauna ever seen in games."

According to The Hollywood Reporter's Patrick Shanley:

"The game is a sweeping masterpiece of innovation and an enormous leap forward for gaming as a whole."

That may have come at a cost.

Comments by Rockstar co-founder Dan Houser about his team working "100-hour weeks" in the lead-up to the release of the game triggered controversy, and sparked a nascent union movement within the gaming industry.

Mr Houser later clarified that it was only his senior team members that were working that hard.