Much of what makes Valve Software’s "Half-Life 2: Episode One" and Ritual Entertainmen’s "SiN Episodes: Emergence" so fun stems from their relative brevity as so-called episodic video games.

Instead of a game that never ends or take months to complete, these bite-sized chunks of digital storytelling took me about four hours each from start to finish.

"Half-Life 2: Episode One" follows up on the popular science fiction franchise starring the bespectacled Gordon Freeman, quite possibly the world’s deadliest physicist.

If you’re new to the story, you might want to play through the original "Half-Life" and "Half-Life 2" games before picking up this latest chapter. Not doing so means you’ll be missing out on the back story of one of video gaming’s great sagas.

This first episode picks up where "Half-Life 2" ended: the towering alien fortress you and female friend Alyx managed to infiltrate is about to blow in a very big way. Your job this time is to escape from the crumbled ruins of City 17 and into the countryside before it’s too late.

Like previous games in the series, "Episode One" doesn’t bother with so-called cinematic cutscenes you have to sit back and watch. Instead, the story is told through real-time interactions with the environment and in conversations with the lifelike game characters.

Interactivity is a real highlight.

Aided by an ingenious weapon called a gravity gun, Freeman’s ability to manipulate his surroundings is not only fun — it’s required to get passed certain obstacles.

Use the gravity gun to pick up a rusty iron radiator — it makes a good bullet shield. If you’d rather just get rid of enemies all at once, there’s an endless supply of conveniently placed oil drums which pack an impressive explosive punch when picked up and thrown.

Some might be frustrated by this quick game and the cliffhanger conclusion. But it’s a very intense experience, and I came away satisfied, still dwelling on the story that had sucked me in so deeply.

While "Half-Life 2: Episode One" brings a near perfect blend of story-driven action and puzzle-solving, "SiN Episodes: Emergence" is a much more straightforward and gorgeous shooting gallery.
As the head of a security force in fictional Freeport City, you spend the entire game as John Blade.

His is a raunchy future world where endless waves of security guards (and later, a host of ugly mutant beasts) must die as part of a personal crusade to crush the evil — and outrageously proportioned — corporate scientist Elexis Sinclaire.

With its mindless foes and underground sewer levels, "Emergence" took me back to the good old days of first-person shooters.

But I couldn’t help wanting more options.

The weapons selection, in particular, seemed too limited. (My vote? Gravity guns for all games!)

This lack of variety is a shame, considering how shooting everything in sight is how this game is won or lost.

Stat junkies will appreciate the tracking system built into "Emergence," which continuously collects an array of data about your play style, from shooting accuracy to the percentage of time spent in combat.