It came just hours before Microsoft's rival Sony raised the curtain on its new PlayStation 4, which will be sold for £349 in the UK.
Sony also confirmed that it will not impose any restrictions on second-hand games.
Microsoft's presentation saw the unveiling of XBox One games, with a mix of legendary franchises such as Metal Gear Solid and Halo together with a clutch of new titles.
It also introduced new features such as Twitch, which will allow players to broadcast their gaming sessions live online.
Video games expert Daniel Krupa, who writes for entertainment website IGN, said: "At £429, the Xbox One will be an expensive investment when it launches in November - but Microsoft's wide array of games was a clear statement of intent for those who worried it might focus too heavily on the entertainment features.
"They have significantly invested in a wide range of gaming experiences, from triple-A blockbusters to quieter indie titles, and games for kids.
"From what we've seen so far, both Microsoft and Sony want to make next-gen gaming a more social experience, even allowing you to broadcast your gaming session live to the internet.
"The price is high, but the Xbox One right now has bags of functionality and promise.
The XBox One, described as an "all-in-one system" for games, live television, films and music, was first unveiled at Microsoft's US headquarters in Redmond, Washington, last month.
It incorporates a blu-ray drive, the use of video calling service Skype, and an upgraded Kinect camera which allows the device to better analyse body movements.
Sony offered gamers a first complete view of its new PS4 at E3, following a sneak preview that revealed some details earlier this year.
It was the first major game machine the Japanese firm has built since the PlayStation 3 went on sale in 2006.
Meanwhile, Apple also made a third major tech revelation as it showcased its newest operating system at a developers conference in San Francisco, California.
Microsoft yesterday also unveiled new games for its XBox 360, which was first released in 2005, after the company said it cared about gamers' investment in the console.
Stuart Miles, who runs tech website Pocket Lint, said he had been surprised by the sheer number of games that Microsoft presented today.
"They are still relying on the Halos of this world, but there are also nicer, smaller titles which shows they are not just regurgitating sequel after sequel," he said.
Asked about the pricing of the XBox One, he said: "Whether they are pushing the outer limits of what people can accept is debatable, but there is a lot of tech in there so they have to price it that way.
"It is a tough sell but the reality is, if you want it you want it, and that is probably the price it should be - and there is the appetite and the games to go with it."
Referring to the "console wars", Mr Miles said: "I think Sony's is the more exciting presentation because they have got the new box to launch and there is more still to come, whereas people kind of feel they know everything about the XBox One by now.
"But that could all change in a matter of hours."
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