"He's your special Bat-Friend"
Planetary/Batman - Night on Earth is the best of the Planetary cross-overs. Warren Ellis honors both his Planetary crew and Batman without the cost of dumbing down any of the characters.
What I enjoyed most about this comic is that is its like an essay of the importance of Batman. Is Batman an Icon or a person? That topic has been a hot button with Grant Morrison's long run on Batman and the related books. This comic feels like Ellis is saying Batman and Bruce Wayne maybe one of the same, but the Icon is more important. Dick Grayson didn't wear the Cowl when this comic was written so we can't know for sure what Ellis had in mind.
Why I believe Ellis is making a statement Batman before Bruce Wayne is that this comic is about the mulitverse and how Planetary works in the DCU. There is a Gotham in the Wildstorm universe according to this story and it is on earth and has a Batman. In this Gotham there is a "Bleed" in the Multiverse and other The Batman is being switched from different incarnations. There is scenes from 1939's Detective comics #32 where Batman still held a gun. The Frank Miller Dark Knight version appears with the Bat(tank)mobile included. There is the whimsical Adam West Batman, also there is the classic light blue and gray Batman with the yellow circle logo and more. Many versions of Batman are present, yes they are all a form of Bruce Wayne, but not all of them are glamorous. All the versions are seemly used to show the importance of Batman on Gotham. He can be a vigilante sure, a deputized policing force in some versions and even the heart of the City like in Frank Miller's version.
What made this book good is that it seemed more about Batman and his importance over "look at my Team, I call them Planetary" which hurt the other two crossovers a little bit.
If you can find this prestige I suggest picking it up since its the only one I would keep separately. If you can't find it you can always pick up the Planetary Crossing Worlds trade.