The subject of Arkham Asylum is one I've covered well on these pages, perhaps too much, but I just can't help myself. I just spent the passed half-hour in a challenge room and it got me thinking about the upcoming sequel and what changes/additions should be made. I'll try to be brief and simple.
1) Players should now be given the option to create their own challenge rooms. They should be able to select the map, number of waves, number of enemies and types of enemies in each wave, as well as any other specifications that either increase or decrease the difficultly. It would also be nice to see a co-op feature enter the equation (just in challenge rooms, however. I'd like the campaign to be co-op free, mostly because Batman is coolest when he works alone and they need to stick with what they created in the first game). However, imagine bodies flying through the air as you and your friends, as Batman, Robin, Batgirl, and Nightwing tear into a barrage of thugs. Seeing how your friends play in the same room and competing for the high score in the same match is a feature that will likely find its way into this franchise at some point. Working together to perform special co-op takedowns could also result in some amazing animations.
2) The Batcave should play a larger role this time around. In Arkham Asylum Batman's on-site Batcave is this glorious little gem of an area that is brought into the mix at two perfect and pivotal moments and it really breaks up the gameplay nicely. You could return at any point to it but there's no real purpose to doing so beyond staring at it and feeling a little more like Batman. It's there for purely aesthetic and fan-service reasons, and that's just fine. But in Arkham 2 it would be nice for the Batcave to function as it does in the comics and the films, Batman's home base.
In terms of the actual game, The Batcave should be a dynamic options menu, basically an interactive menu screen by way the player gains access to all other areas of the game. It's a gameplay hub essentially. Want to go into challenge rooms? Well now it's not just an add-on multiplayer feature you select on the main menu, it actually serves a purpose within Batman's world because the challenge rooms are really just simulated combat training programs that take place in the Batcave. So if you want to take part in one you guide the Dark Knight through his cavern to the challenge room area and you step on in and from there you choose the simulation you want.
The way this can further feed into the actual campaign is by allowing the player to gain certain amounts of experienc in the challenge rooms, thereby allowing them to unlock better moves and new technologies.
There should be an incentive and a reason to return to the Batcave. Players, when out and about the confined and prison-like Gotham the teaser trailer suggests, should be able to call up The Batwing or Batmobile on their communicator and then take off back to the cave for fresh supplies, maybe a chance to fix up the suit, and do some research into the latest quest. This would work better if the damage system were altered a bit. Instead of Batman taking visual damage after key moments in the story, the wear and tear on the suit should occur organically during gameplay, kind of like how your character in the Fable games gets scarred. Take one too many punches over a period of several hours and the crusader will start to look pretty torn up. You can continue playing, of course, but the effectiveness of your armor will be reduced. Return to the cave for a fresh suit, maybe make some power ups while you're there, and you're up and running again and can receive a lot more damage. Don't take a lot of damage out in the field, however, and you'll receive some bonus XP and maybe work your way to a hefty achievement and a cool unlockable.
Players should be able to call up Alfred or The Oracle and get their help/advice on the forensic bits, but if players want to really delve into the Dark Knight's detective skills they should be able to return to The Batcave and do so. My point there is that players shouldn't be forced to return to The Batcave every time they find a new clue, that would make it frustrating and interrupt gameplay. Going to the cave would become an obnoxious chore. But it should be there for us to access at any time, and it should act as a place for pure Batman-fan enjoyment as well.
Detailed files on all the comics characters should be accessable there, as well as audio diaries, fun facts, and cool little interactions with the various trophies Batman has collected over the years. So, it is essentially still there for mostly aesthetic reasons, it simply serves a greater purpose, makes use of an innovative interactive menu system, and acts as a hub for all game data and the like. So instead of sorting through diaries and audio logs by pressing the start button, players actually take control of Batman and sit down at his computer to sort through such information. Instead of trophies being an option on the main menu, you take Batman into his trophy room and examine them. Certain data, like the audio logs and such, should be accessible in the field, but it shouldn't be as simple as pressing start and whooshing off into a menu screen. Players should press start and then the perspective should switch to a first person view and we see Batman look down on the monitor on his gauntlet where he can cycle through info while out in the field fighting crime.
This would simply be a nice touch that would enhance player immersion and make them feel that much more like the ultimate badass.