The keyboard will be missing some of the features that Google unveiled during the launch, such as voice-to-text functionality (perhaps in a later update?), but otherwise it appears to be pretty much the same experience that you will be able to get on ICS. The keyboard will be an improvement over Gingerbread’s and will sport enhanced prediction/correction, with the ability to suggest names from your contacts if it thinks you’re talking about that person.
The download and its instructions is available from the XDA forums, and once again this will be downloaded entirely at your own risk. If you feel that this is a little over your head, perhaps you might want to wait for the official update for your phone.