3D Vision, PhysX
It's an artist's rendition of the effect -- but a pretty accurate one
I've always been skeptical as to the value of 3D gaming, but I found myself liking 3D Vision more than I expected to--it's significantly better than the 3D I saw from Lenovo's Y560D.
Unfortunately, it's impossible to post screenshots of how 3D mode changes the game, but the added depth improves two fundamental characteristics. First, it's easier to judge the exact position of enemies relative to yourself. This might sound like a small thing, but much of Arkham City's combat relies on chaining combo moves together and properly using gadgets to confuse, distract, and scatter numerically superior forces.
Second, soaring over Arkham City and exploring its environments is even better looking. Is it enough to justify buying a new 27" display? Maybe not--but in Arkham City, at least, it's more than a gimmick. The 3D Vision support in this game is among the best we have seen. Even the cut scenes are 3D.
Without PhysX, there's no smoke effect at all. With high PhysX, the papers roll blow along the ground.
Hardware PhysX support is another major feature of Arkham City (if you own an Nvidia graphics card). AC uses PhysX well, and it's particularly effective in 'High' mode, where it's used to model newspapers and other bits of detritus sweeping down the poorly lit city streets.
Both of these capabilities have existed in NV cards for quite some time, and we don't expect Arkham City to suddenly sell an ATI user on swapping for Team Green--but if you want a game that shows off some of the features NV has spent a great deal of time polishing, this is a good one.