Pong

SMB 1 because it launched an entire brand, genre and industry that's still thriving four decades later.

My top three would be Super Mario Bros., The Legend of Zelda, and Halo: Combat Evolved. Each one satisfies the following criteria:

• Great game
• Launched a huge, successful franchise that continues to this day (although Halo post-2010 is more than a little shaky)
• Helped change the rules and expectations of the genre
• Helped secure a console maker's place in the game industry

If we're just identifying the highest quality game that started a series, then I vote Deus Ex.

Bioshock stands out for me as one where they made (IMO) one of the best games of all time on their first attempt, with its amazing setting, story, and plasmid-powered gameplay.

The first Mass Effect and Bayonetta were also incredible for the former's rich universe and engaging blend of action and RPG mechanics, and the latter's awesome style and fluid combat.

I think its mostly generation launch window games. Because that's when you saw amazing new visuals.

Sonic, Mario World, Mario 64, Sonic Adventure, MGS2, GTAIII, Halo, Bioshock, GTA4. The last time I really felt impressed by graphics was Uncharted 4. Beyond that has been diminishing returns.

I feel like I worded the thread in a confusing way; by an IP debut I basically meant "series that had the best debut game", so not games like Sonic Adventure or GTA3 which aren't the first.

Horizon zero dawn.

Guerrilla games went from making mid First person shooters (killzone) that barely sell 2 million copies to 3rd Person open world action adventure that has gone on to sell over 25 million copies and has become a high profile Franchise for Sony that is on par with some of the most popular open world franchises like the Witcher, Elder scrolls or Zelda.

The world of Horizon had deep sci fi lore, amazing creature design, great narrative and gameplay loop all with absolutely zero experience in 3rd person narrative driven open world action adventure.

It is quite impressive for a studio that was considered low tier upto that point.

Killzone 1 was mid, but Killzone 2 and 3 were excellent I thought, the feeling of fighting for survival in a hellish dystopia was terrific.

Ultima ('81)

First game that came to mind was Gunstar Heroes. Not only is it the best in its franchise but it was also the debut game of developer treasure and they smashed it out the park.