Who doesn’t love the Half-Life Barneys? Black Mesa’s plucky security guards are always ready to help the player, whether by opening a locked door or rushing into battle with nothing but a 9-mm pistol. Blue Shift, the latest side-sequel by Dallas-based Gearbox, casts the player as Barney Calhoun, a security guard at Black Mesa who’s just pulled some very unlucky duty. See, Barney is chosen to work in the Anomalous Materials lab. The danger of each assignment is rated on the old ROY G BIV light-color scale, hence the Blue Shift title.

There’s some humor there: In astronomy, a blue shift means a light source is moving toward the observer. Soon enough, an very alien light is moving toward Earth: Barney is sent to Sector G to help fix an elevator, just as Gordon Freeman and company begin their experiment on the alien crystal. Two worlds collide, and Barney finds himself trying to locate Dr. Rosenberg, who may be able to help Black Mesa’s citizenry escape the invasion.

As promised, Blue Shift does clear up a few questions left over from Half-Life. No, we don’t learn the Man In Black’s identity — he’s only in one cameo that we could find so far. But did you ever wonder why there were already aliens in cages during the first two games? Now we know: Rosenberg and his team predate the Lambda Complex teleport project. See, to teleport around the Earth, one has to first go through Xen.

That means our hero finds himself on Xen to fix a beacon that will let Rosenberg & Co. teleport out of Black Mesa (though thankfully the game returns to Earth afterward). What happens next? Find out on your own. We just hope this signals the end of the games taking place at the same time, and that Valve moves on to a true sequel.

Why all the plot musing? Because this game is short. It was originally designed as an add-on for the Dreamcast version of Half-Life, and expanded just a little to be sold as a PC stand-alone. Don’t frown — this new chapter is also bundled with Opposing Force and, even better, a high-definition graphics pack. Characters (both human and alien) and weapons are absolutely stunning with the HD update. All fans must have it.

Gameplay is just what Half-Life veterans should expect. There are some hard puzzles, and minor jumping games, but mostly it’s gun-and-run, with almost a surplus of ammo lying around. In fact, the combat is a little too easy, considering the lack of big bosses. We do wonder why more Barneys didn’t kick ass during the first two games, considering the damage our hero inflicts in this chapter.

Here’s one more incentive to buy: If you already have Opposing Force, Sierra will buy back the CD-ROM for $10. Just get Blue Shift (again, it contains Opposing Force) and send the receipt and your original OpFor CD-ROM back to the company. You’ll still have the sorta-sequel to Half-Life, plus the awesome HD update and a pretty fun (if short) new chapter in the story.