However, the final retail game has far more varied backgrounds and the more you play, the more noticeable the differences become. Similarly, the more subtle effects that the Xbox 360 gets, such as the ambient occlusion, also become more evident, in this case serving to give the game's visuals more depth. Over and above that there are texture differences too: there's a slight downgrading of some detail on PS3 (only really noticeable on close-ups) and the normal maps have taken a knock. Also quite bizarre is the fact that the camera work on PS3 has been subtly altered in many situations: the view has been pulled back, changing the look of many of the cut-scenes.
Raw performance, in terms of the sheer number of frames being pumped out, is very close indeed between the two consoles - but once again, the Xbox 360 version offers the smoother, more visually coherent experience. Both games are locked at 30FPS, and will drop v-sync in order to maintain that smoothness as much as possible. The introduction of tearing is what sets these games apart: it's rarely noticeable on Xbox 360 (though it is there), but is far more apparent on PS3 in certain areas; generally speaking, the larger the gameplay arena, the more tearing you'll get.
The performance deficit on PS3 probably won't be noticed by many, and will be irrelevant if you don't have the Xbox 360 or PC games to hand as points of reference. And while the differences are technical realities, the impact this all has on the gameplay is thankfully minimal. Where it counts, each version is just as much fun to play as the other. Indeed, PS3 claws back some brownie points is via its exclusive PSN download content: the Joker Challenge Rooms.
By default, the game gives you plenty of challenges "out of the box" regardless of the platform you play it on. Aspects of the Arkham Asylum geography are exploited for specific tasks - usually involving all-out fighting or more involving stealth-style gameplay. The big difference is that a 107MB download from PSN opens up exclusive challenges for the PS3 where you get to "be" the Joker. The success of this bonus content is somewhat double-edged, however: the whole gameplay concept behind Arkham Asylum is built around Batman: who he is, what he does and how he does it.
There is a definite sense that the Joker character has been shoehorned into that concept and the result is less satisfying. It's entirely in keeping with Batman's character that he would engage a gang of cons head-on and defeat them all, seeing that he is one of the DC universe's pre-eminent martial artists. Witnessing the Joker do the same doesn't quite compute: he's more of a thinker than a fighter, a fact brought home by the single-player mode's excellent storyline. While the idea doesn't seem quite right, there are a number of great things about the DLC over and above the plain and simple fact that you're getting more content for free. There's new voicework from the Batman cartoon cast, and the Joker does have some nice toys to play with, including an enormous single-shot pistol. Plus you get the chance to repeatedly pummel Commissioner Gordon.
Console-wise then, you pay your money, you take your choice. It's content versus performance. In terms of personal preference, I'd take the performance over a nice, but not essential bit of bonus DLC, but fair play to Eidos and PSN for a canny bit of marketing - there is the sense that in terms of the gameplay you're only getting the full thing on PS3 and that's a powerful motivating force in what is the undoubtedly the biggest game of the summer.