Microsoft is under a lot of pressure to have its Xbox One make up ground against Sony's PlayStation 4.  (AP Photo/Nam Y. Huh, File)

The gaming world is set to throw its biggest party of the year, with the Electronic Entertainment Expo, better known as E3, planning to show off the best in video games this week.

The conference officially starts on Tuesday, but Microsoft started the ball rolling Monday with its annual Xbox conference, where it announced that it will re-issue all of its past major Halo titles in one set this November, as a set-up for the release of Halo 5: Guardians in 2015. The company focused entirely on games during its press conference, also showing off some scenes from the new "Tomb Raider" series that explores the early days of its protagonist, Lara Croft.

The conference set the tone for what's sure to be a week of big announcements for the gaming world. Here are three big trends we're expecting to see out of E3 this year:

1) Game announcements. "Um, duh," you may be saying. But the past couple of years of E3 have really been focused on hardware with the splashy announcements of  the Nintendo Wii U, the Sony Playstation 4 and the Xbox One. New console generations only launch roughly once a decade, so it made sense to focus more on that major paradigm shift than on the games.

But this year should see a return to form, and offer gamers clues about what developers can do with all that much-touted technical improvement now that they've had some more significant time to actually work with it. That means we'll hear more about some sequels to long-standing franchises -- including "Halo," "Call of Duty," "Metal Gear Solid," "Uncharted" etc. -- and also some original titles such as "The Order: 1886" and "Sunset Overdrive."

Plus, of course, we'll continue to learn about whatever games have managed to make it this far without being previewed or leaked.

2) Virtual reality battles. Game companies are chasing one of the greatest dreams of the sci-fi crowd: affordable, accessible access to virtual reality technology. No, we're not quite at the "holodeck" level of the technology, but Facebook's Oculus Rift and Sony's Project Morpheus are definitely the most advanced, closest-to-market versions of home virtual reality that we've ever seen.

Developers are just starting to make versions of existing games for these headsets and to show some more serious prototypes of what they can do when they design specifically for this new kind of platform. That should make this the space to watch over the next couple of years, and we'll see the seeds of it at this year's convention.

3) Sony ascendent. Sony may not be in a great place as an overall company, but it is killing it in the gaming world right now. Not only has the PlayStation 4 consistently beat out the Xbox One in worldwide sales, but the firm has also recently passed Nintendo as the most successful gaming hardware company in the world. As reported by the Nikkei Asian Review, a Japanese business publication, Sony's combined sales for the PlayStation and Vita lines passed Nintendo's combined handset and console sales for the first time in eight years.

Sure, that is partly because Nintendo's sales have been flagging -- that company is also sailing in rough waters, financially speaking, having just reported its third annual loss -- but it also speaks to just how much of a success the PlayStation 4 has been.

But just because Sony is doing well now doesn't mean that they're guaranteed to win this round of the console war. Their advantage lies largely in pricing, which Microsoft has decided to address by unbundling its Kinect controller from the Xbox One to be competitive with the PS4. As always, it will come down to the games, putting pressure on all the firms to show off titles that make it worth buying one system over the other.

Other things to watch:

Chances are we'll see a few trends from last year's show, such as the larger presence of games from independent studios and more experiments with the way games are priced. Gaming is a fast-growing industry, and more people identify as gamers now than ever before. That means there's a lot of room for companies to experiment with how they convince players to play and buy their games.

There are plenty of new types of companies attending and exhibiting at this year's show -- namely, a larger representation of "casual" gaming companies that focus more on smartphone or tablet games than console titles. That's a space that's going to particularly interesting to watch as companies such as Apple and Google build more advanced gaming capabilities into their operating systems and products. With those new formats come new pricing structures, whether it's a super-low-priced but high-quality title, or a free-to-play game that makes its cash by up-selling players with items in the game.

This post has been updated to include information from Microsoft's press event.