At its best, PlayStation 3 and PlayStation Portable exclusive “ModNation Racers” is a worthy challenger to the “Mario Kart” throne. With fast, arcadey kart racing, a cute art style and an impressive box of tools for creating custom racers, karts and tracks and sharing them online, it ups the ante for an entire genre. Diehard fans of Nintendo’s classic series might find that the infinite possibilities for customization keep them from ever going back to their original love, especially given that some players are even using “ModNation’s” editing tools to create pretty convincing replicas of Nintendo’s mascots for use in your games.

In "ModNation Racers," you'll use power-ups to attack your opponents and gain temporary speed boosts.

But at its worst moments, “ModNation Racers” (rated E, $60 on PS3, $30 on PSP) feels like it could’ve used an extra month or so of development time. While the kart-handling in the PS3 version feels just about perfect, the gameplay’s biggest issue is problems with collision detection between kart and course – video game speak for the game’s not behaving like players expect when the two come together. For a fast-paced racer in which timing and nuance can mean the difference between finishing first and finishing eighth, it’s an infrequent but not insignificant issue.

In the single-player game, which has a largely forgettable story replete with irritating announcers, you’ll learn the ropes and hone your skills on 28 prebuilt tracks. This career mode can occasionally irritate, as the races require a Top 3 finish before you can unlock the next event. With classic, kart-racing-style computer foes who seem tethered to you by a rubber band no matter how fast you go, the fact that you unlock only one track at a time makes for monotonous racing in spots, which is compounded by repeated dialogue from the announcers and your mechanic. At some point, you’ll inevitably get stuck on a particular track, racing it over and over and mentally reciting lines of dialogue from memory until you decide to sleep on it. This’ll probably happen on one of the five championship stages, which require first-place finishes.

Maybe the most jarring thing about the single-player game is the way one of the announcers, Biff, mocks you when you don’t win a race. Granted, I’m an adult and can take it when a game tells me that was some “bad, awful, terrible” racing. But “ModNation Racers” is an E-rated game. I’m not one of those people who thinks kids constantly need to be told they’re special, fantastic, unique little angels, but I’m not convinced there are any merits to mocking them over and over again for their failures. There’ll be plenty of time for that when they get older.

Of course, if you spend all your time playing solo, you’re missing the point. “ModNation Racers” is meant to be played online, and its robust content creation tools are easily its most perfectly honed, well-executed feature. When I previewed the game earlier this year at the Game Developers Conference, its creators were quick to point out that the tools shipped with the game were used to build all of the tracks on the disc. In other words, if you’re an avid player with an interest in game design as a career, “ModNation Racers” and Sony’s other “Play Create Share” title “LittleBigPlanet” are mandatory.

You can use the "autopopulate" feature to fill in the scenery around your track, or carefully build each detail yourself.

The content creation tools are brilliantly simple. To build a track, you just “drive” a paver around using controls similar to what you’d use to race. If you get tired of paving and just want to finish your track, you can just hold down a button, and the game will complete the loop for you. Once you’re done, you can fill in all the scenery and add power-ups and weapon pods yourself, or use a feature called autopopulate, which fills in everything for you. (You can still tweak whatever the computer gives you.)

Once your track is ready for prime time, you can publish it online, where other players can try it out and offer feedback. (You can then use that feedback to continue to refine your creation.) But it’s not just tracks you can create; similarly easy-to-use software lets you create custom racers and karts. (Sadly, the most popular ones aren’t innovative creations, but convincing knockoffs of licensed characters such as Mario and Iron Man, and such vehicles as the “A-Team” van and Mystery Machine. Whether copyright holders view this as free advertising or infringement varies from case to case, I suppose.)

“ModNation Racers’” content-creation and community features would be enough to vault it into Game of the Year consideration, were it not for its confounding menus, poorly highlighted features and the aforementioned collision detection problem. None of these issues are game-breaking or even especially problematic in their own right, but combined they function to take the game down a notch from “great” to “not quite there.” Hopefully these issues will be ironed out with a post-release software patch or in a sequel. It’s irritating that I played the game for close to 10 hours before I discovered, by reading in an online forum, that you could tweak the way karts handle by pressing a certain button when you’re in one particular area of the game. It takes a lot of time to discover all the features packed into “ModNation Racers,” but the time you put in learning the ropes pays off tremendously.

Though the bulk of my time was spent playing the PS3 version of the game, the capability of the handheld version surprised me. The PSP build was developed by a different studio from the main game, and the karts therefore handle a bit differently. Because of obvious differences in processing power, you’re not getting the same beefy content-creation tools you get in the console version, either, but given that “ModNation Racers” costs half as much on the PSP as it does on the console, you’re getting your money’s worth. The similarity in story and included racetracks between the two versions is a little disappointing. If you’re buying the PS3 and don’t do a lot of handheld gaming, it’s probably not necessary to spend the $30 on the PSP game, but if you’re looking for a fun little racer to play during plane trips or for your kids to play in the backseat of the car, “ModNation Racers” is more than capable.

During the several levels I played of the PSP version, I didn’t encounter any of the problems I had on the PS3, where my kart seemed to occasionally hit a phantom bump, or the game failed to detect right away that my kart had steered off the course. But I didn’t sink in enough hours to say definitively that the PSP version is problem-free in that regard.