The 2000s were a transformative decade for the video game industry, marked by the rise of 3D graphics, online multiplayer gaming, and the emergence of gaming as a mainstream form of entertainment. 

1. "Half-Life 2" (2004)

"Half-Life 2" is a first-person shooter developed by Valve Corporation. It received widespread critical acclaim for its immersive storytelling, innovative physics-based gameplay, and impressive graphics.

The game's protagonist, Gordon Freeman, battles against the alien Combine regime, and the game's use of the Source engine set a new benchmark for visual fidelity and interactivity in gaming.

2. "World of Warcraft" (2004)

Blizzard Entertainment's "World of Warcraft" revolutionized the massively multiplayer online role-playing game (MMORPG) genre.

The game provided an expansive, immersive fantasy world for players to explore, complete quests, and engage in player versus player combat. It set the standard for MMORPGs and attracted millions of players worldwide, solidifying its status as a cultural phenomenon.

3. "Grand Theft Auto: San Andreas" (2004)

"Grand Theft Auto: San Andreas" by Rockstar Games expanded upon the open-world formula of its predecessors, offering players a vast, fictionalized version of California to explore. Its compelling narrative, diverse gameplay mechanics, and expansive open world set a new standard for sandbox gaming, making it a beloved classic.

4. "The Elder Scrolls IV: Oblivion" (2006)

Bethesda Game Studios' "The Elder Scrolls IV: Oblivion" set a new standard for open-world role-playing games.

With its detailed environments, intricate quests, and deep character customization, the game immersed players in the fantastical realm of Cyrodiil. It showcased the potential of emergent storytelling in open-world games and laid the groundwork for future titles in the series.

5. "BioShock" (2007)

"BioShock" by 2K Games combined first-person shooter gameplay with thought-provoking narrative and philosophical themes.

Set in the underwater city of Rapture, the game's immersive atmosphere, morally ambiguous story, and innovative gameplay mechanics garnered widespread acclaim and established it as a hallmark of narrative-driven gaming.

6. "Portal" (2007)

Valve Corporation's "Portal" introduced players to a mind-bending puzzle game with a darkly humorous narrative. The game's innovative portal-based mechanics and engaging storytelling captivated players, earning it praise for its creativity and design.

"Portal" demonstrated that games could deliver compelling narratives alongside challenging gameplay, setting a new standard for puzzle-platformers.

7. "Call of Duty 4: Modern Warfare" (2007)

"Infinity Ward's "Call of Duty 4: Modern Warfare" redefined the first-person shooter genre with its modern-day setting, cinematic storytelling, and addictive multiplayer mode.

The game's gripping single-player campaign and robust multiplayer experience set a new standard for online competitive gaming, influencing the design of future shooters.

8. "Mass Effect 2" (2010)

BioWare's "Mass Effect 2" combined action-packed gameplay with deep role-playing elements and a branching narrative.

The game's compelling characters, impactful decision-making, and cinematic presentation set a new bar for storytelling in action RPGs, solidifying its status as a modern classic.

9. "The Legend of Zelda: Twilight Princess" (2006)

Nintendo's "The Legend of Zelda: Twilight Princess" captivated players with its expansive world, engaging puzzles, and epic storytelling. Its seamless blend of traditional Zelda gameplay with a darker, more mature tone resonated with fans, making it a standout entry in the beloved franchise.

10. "Red Dead Redemption" (2010)

Rockstar Games' "Red Dead Redemption" transported players to the dying days of the Wild West, offering a richly detailed open world filled with compelling characters and gripping storytelling. 

Its immersive setting, morally complex narrative, and innovative open-world design set a new standard for western-themed gaming, leaving a lasting impact on the industry.