Spoiler Alert: Hydrophobia on Xbox Live Arcade? Pretty much the opposite of a good game.

This game really needs a good plumber. Know any?

I know I'm taking a bit of a risk saying so, but I can't name one element that worked or even made much sense. Picture the shakier Tomb Raider installments bumping ugly with The Poseidon Adventure, surgically remove Lara Croft's personality and hand her a laughably underpowered sidearm, then screw with the control map for no reason. That's Hydrophobia. Ten minutes in, any barely lucent person will wonder how developer Dark Energy Digital could crowbar so many bad decisions into one game.

It so happens I know the answer. They had a gimmick. But somewhere along the line, they forgot a vital rule for success: The gimmick is not the game.

To be fair, you need a gimmick in your game. And if we're talking about a new franchise, you need a really good gimmick, otherwise even a masterpiece can vanish in a crowded market, unmourned and unloved. In Hollywood they call it "high concept," but whatever label you pick, something's got to grab mindshare and keep people excited. BioShock's retro-futuristic setting. Limbo's art direction. Borderlands' gonzo gun-a-thon.

Hydrophobia has a gimmick...a fairly decent one, too. It's on page one of Dark Energy's press materials, right in the first sentence: "Hydrophobia is a revolutionary title, thanks to ground-breaking technology." Specifically: The HydroEngine, "the world's first fluid dynamics game engine, which model [sic] flowing water realistically, resulting in the most dynamic and dramatic gameplay you have ever seen."

Not really. Basically, you're trapped in a flooding ocean liner under terrorist attack. A luxury liner, incidentally, littered with explosive barrels. Forget water; Hydrophobia drowns in clichés.

Now, is it fair to compare one of the worst games of the year to one of the best from the last decade? No. But I'm going to do it anyway.

They died for our sins.

Portal, Valve's 2007 brain-bending puzzler, is another short (now downloadable) game with a female protagonist and one heavily emphasized gimmick...a gun that creates instant-travel wormholes to help you navigate a series of traps. Regardless of which idea sounds better, Portal's works better because it actively engages the player. You make portals to play Portal. By contrast, Hydrophobia's water exists mainly as set dressing. It's possible to completely ignore the advertised "unique flow combat" and indeed, several major set pieces are bone dry.

Why make the best idea in your game optional? Particularly when it's the only idea. Subtract Hydrophobia's realistically dynamic water, and nothing remains to fall back on. It's empty.

A gimmick, no matter how clever, isn't enough. It's a starting point. Valve constantly layered fresh concepts onto their central portal mechanic until physics-cheating stunts that never entered your head in the early stages became instinctive tactics. Then they threw in GLaDOS, the deranged A.I. who acts as your guide, foil, entertainer, and adversary to frame the entire experience. Rarely did 15 minutes go by without players experiencing something new.

Bleeding edge technology.

Dark Energy could've done that. Clearly, they had more fuel in the tank. Check out their game's Challenge Room, where you directly control water to splash and dash enemies like a vengeful god. It's also not fun, but at least I can see it going somewhere interesting in a game built around fluid manipulation. Plenty of potential there.

Unfortunately, a lot of games depend entirely on that one random gimmick to give them an edge, and it rarely does. Fracture (limited terraforming powers) and Singularity (limited time manipulation) spring instantly to mind, and I'm similarly wary of Brink (another boat-based shooter). I can also easily picture the dozen horrible games Portal could've been in lesser hands if it only involved shooting holes and walking through them. Hydrophobia never left that stage. It should've.

It's perfectly fine to base an entire game around a single concept, but you can't stop there. Make that conceit central to the whole experience and keep adding good ideas to your great idea. That's the trick, really...and the best gimmick of all.