Combat Evolved was a classic back in 2001 and it still amazes us today.

On the faithful day of November 14, 2001, Halo: Combat Evolved was released, revolutionizing the way console first person shooters work even to this day. For it's time, this game was epic. And by today's standards, it still is a hit.
You play as Master Chief, the supersoldier taken straight out of Cryogenics and into the battlefield. You work for the USNC, an organization built to save the universe from an alien race known as "The Covenant" by whatever means necessary.
Along with you is a digital (but real) companion named Cortana. She guides you through the game via a chip in the back of Chief's head.
You have to fight your way to finding Halo, a planet that controls the fate of the universe. But of course, you guys aren't the only ones who want it. You didn't have any business with Halo until the Covenatn gets involved. They want it to rule the world. You have to stop them.
If the Covenant wasn't enough trouble for you, then meet The Flood. They're an infectious army of monsters that were made to kill everything, Covenant, humans, everything.
There is a decent array of vehicles, including the Warthog, the Ghost, the Banshee, and more.
You can use lots of weapons, even from The Covenant's weaponry.
A somewhat lengthy Campaign (ten missions, each should take between a half an hour to a full hour) can make for some great time spent on it. There are four difficulty levels for the Campaign (Easy, Normal, Heroic, and Legendary), so if you beat it once, go again!
There are a few downsides.
It can at times seem your health won't regenerate fast enough.
A lot of the missions' areas are very similar and get a little tedious after a while.
The slightest (and I do meen slightest) bump from a moving vehicle is an instant kill, even if a mounted turret rotates and hits you, you die. Even if you have full health and shields you'll die. That can get very frustrating.
There is no online multiplayer for the XBox version, only the PC version. But there is split-screen with four players even for the XBox.
So in summary, Halo: Combat Evolved is a classic that won't go forgotten. If you liked any other Halo game, give this a try. Or if you like shooters, give this a try. Or if you like any video game at all, you need to try this game!