Chances are if gamers had an encyclopedia or dictionary, the entry for "learning curve" would have a big, bright color picture of Geometry Wars plastered next to it. The game does its best to define the quick and merciless rise in difficulty characteristic of good top-down shooters. Despite its title, Geometry Wars: Retro Evolved 2 is more than just a tough Space Invaders. It's a multifaceted and truly unique take on the genre that makes for hours of competitive fun for anyone with a taste for a challenge. Geometry Wars 2 can be completed by almost anyone, but although the controls are as simple as the shapes that assault you, the gameplay is deep and always changing.

Geometry Wars 2 offers six gameplay modes: Deadline, Evolved, King, Pacifism, Waves and Sequence. The basic formula of fly-and-gun around a rectangle is reproduced in tth Deadline mode, which serves as an intensive "score attack," allotting the player infinite lives, three bombs, and only three minutes to score as many points as humanly possible.

The Evolved mode has you controlling your ship with the left thumbstick, and you have to hold back the ever-increasing swarms of ships by shooting them down with the right thumbstick, and each shape you take down nets you a set amount of points. The Evolved mode allows you three lives and three bombs at the start of each game, and you gain another life and bomb at 100,000 points; 1,000,000 points; 10,000,000 points; and so on. Bombs don't score you any points for the enemies destroyed, but they destroy absolutely everything close by.

The way you really start racking up the points is by collecting Geoms, which are tiny green crystals that are dropped in quantity by each fallen enemy. Geoms add to your multiplier, and your multiplier is applied to any points you earn, so you can gain exponentially more points as the round goes on (and on and on).

Geometry Wars 2 gets really spiced up by the unique challenges presented by the King and Pacifism modes. In King mode, you can only shoot when your ship is located inside of dynamically generated circles. The circles disappear, so you'll have venture around and locate another circle from which to renew your attack. Enemies can't hurt you while you're inside these bubbles, but they can surround you as they wait for your bubble to blink red and finally implode. It's a frantic game of running around, and it's the first chance for players to show off their tricky maneuvering skills.

Of course, they'll really have to polish those skills if they want to make it in Geometry Wars 2's other unique challenge mode, Pacifism. For this mode, the game takes away your ability to shoot. You must avoid shooting, so you kill enemies by leading them through gates, which will close after you pass through them. If you time it just right, the gates will explode at the opportune moment and take out a few enemy vessels. This is the most nerve-wracking and strategic mode in the game, and my personal favorite.

Finally, you're presented with an ultimate challenge with the last two modes unlocked, Sequence and Waves. The former puts you up against 30-second rounds of enemies that come at you in harder and more complex patterns. You get the same number of lives and bombs as in Evolved, but it's not much consolation when you see the lines of enemies closing in on you in a tight circle pattern, again and again. Waves is simple enough in concept: You blow up waves of enemies that are traveling in straight lines as they quickly flood the screen and form an impassible and shifting grid of pointy death. In the old Geometry Wars, a common tactic was to hug the walls to avoid conflict, but in Waves mode, staying close to the walls will guarantee your demise because enemies spawn from the wall and attack you in rows up to two deep.

All these modes provide hours of entertainment to any gamer with a competitive streak. All of your scores are uploaded to a standard leaderboard as long as you're connected to the Internet, and the Achievements are … well, Achievements. Unless you dedicate yourself to shooters, you're not likely to see your name at the top of any leaderboard, but most anyone can achieve everything with a little hard work and practice.

What's really confusing with all this online functionality is Geometry Wars 2's lack of online multiplayer. You can voice-chat with your friends to brag about beating their high scores, but you can't take them on one-on-one to see who's truly the best of the best, and you can't even work together to find out if two heads are really better than one in the game — all from a game that requires you to connect to the Internet to record a score. That's almost unforgivable.

Online multiplayer could have been so much fun, too. Almost every mode has a competitive and cooperative aspect to it, so it could have worked, as long as you can get a group of like-minded gamers with 360 controllers to play it. While it's getting harder to actually pull this off, those who do are in for a heck of a good time. It's really satisfying to watch your score climb near the billions when you dodge, feint and shoot down millions of shapes together with your friends in offline co-op multiplayer. Sometimes, it's even more fun to gang up three-on-one against that insufferably good player and take him down a peg.

Geometry Wars 2 looks great in HD, but in essence, it's still basically a Flash game. You don't need a big screen to enjoy the title to its fullest, even with multiple players, since there is no need for a split screen. Maybe I'm the only one, but I'm getting sick of having to squint just to read text in games these days. It seems like game developers are forgetting that some people can't afford to display in 1080i, and it's good to know that Bizarre Creations isn't shutting out the financially challenged Xbox 360 gamers.

The sound is similarly pretty and about the best you could expect, but nothing too fancy. It's nice, and its generic funk-techno beat matches the on-screen action very well, but it's not Rez or even Patapon. It's not about the rhythm; the rhythm is just an added bonus that's floating around in the background.

All in all, Geometry Wars: Retro Evolved 2 is a nearly perfect experience for a very select crowd. It might even be convincing enough to convert a few non-believers, but it's not perfect. For people without a competitive streak, there simply isn't a whole lot in this package beyond the first playthrough. The lack of at least online co-op is also a major blow to what should have been an ideal package, but it's otherwise, it's easy to recommend Geometry Wars 2 to anyone who's looking for a solid Xbox Live Arcade game.

Score: 8.4/10