The Darkness isn't an especially long game, but by the time you complete it, you'll feel like you've seen a lot.
In addition to the single-player mode, there's an eight-player online mode that gives you the basic first-person shooter modes, like deathmatch, team deathmatch, and capture the flag. You can do some configuring from there, such as turning on one-hit kills. You can also morph from human form to that of a skittering little demon called a darkling, which is weak and unarmed but has a powerful melee attack and can crawl on walls and ceilings. Modes like survivor play off of this; your goal here is to be the last human standing, and death from a darkling makes you join the darkling side. The online is mostly functional, though the game really falls apart when one player is lagging. Your movement becomes erratic and the game becomes basically unplayable. When it works, it's a decent diversion, though it does feel tacked-on. Being able to actually call upon The Darkness and use the powers you get in single-player might have been cool, though having eight players use a black hole at the same time might have been a little too crazy. Either way, it's immediately clear that the single-player is the star of the show.
Visually, The Darkness looks superb. It's got a very smooth frame rate and a large, nicely detailed world. It goes up to 1080p on both the Xbox 360 and the PlayStation 3. The texture clarity is such that there's a secret sequence of phone calls you can hear by reading phone numbers off of billboards and flyers put up around town and calling them from the nearest pay phone. It also has a great art style to it. New York looks appropriately grimy and urban, with a lot of graffiti. And the Otherworld, where you'll spend a bit of time, has a nicely hellish look that applies to both the environments and the enemies you face. Most of the animation is good, and you have to give it up for any game that features motion-captured break-dancing for no reason other than to provide a bit of flavor in one of the subway stations. About the only disappointing aspect of the game's look is that people's lips don't move very much when they speak, which makes some of the dialogue-heavy sequences look slightly off; but that's minor in the grand scheme of things.
Great dialogue and voice actors help the story move along nicely.
The voice acting in The Darkness is universally awesome. You'll encounter plenty of raspy-voiced old-school mobsters who sound like they stepped right off of the set of Goodfellas. Jackie himself comes across perfectly as the tough-guy hit man that he's supposed to be, but he still shows flashes of vulnerability. And then, of course, there's the voice of The Darkness, which is supercreepy and perfect at giving you a case of the willies. Even the random people you run into on the street have believable voice performances. On top of that, the script is really something, so these great voices have solid dialogue to work with. The rest of the sound effects are appropriate, and as you take damage and near death, things slow down and start to sound as though you're underwater, which is a nice effect. The snapping and chomping of The Darkness' twin heads is pretty cool, too. Most of the music in the game is ambient background stuff that helps set the appropriate mood.
The Darkness is available on both the Xbox 360 and the PlayStation 3, and the differences between the two versions are pretty minimal. The PlayStation 3 version seems to have slightly better color than the 360 version, but the 360 version looks a bit sharper. Also, the Xbox 360 version has achievements, and the PlayStation 3 version gives you the same tasks, but calls them accomplishments. Regardless of what you call them, they're evenly spread, with a few that come from winning more multiplayer matches than you'll probably be willing to endure. Overall, both versions are equally recommendable.
The Darkness' appeal comes from its many different parts coming together in a really great way. The believability of the characters mixed with this hellacious demonic force fits together in a really interesting fashion; the gameplay is very satisfying, even if it isn't especially challenging; and the presentation is top-notch. If you're a sucker for M-rated action--and really, how can you pass on a game with a human-heart-eating mechanic?--you'll definitely want to play The Darkness.