I just finished reading through the "For Your Entertainment" thread, and it does indeed look mighty intriguing... that is, if we can rely on the fanbase to get up off their collective behinds and actually put some work into making it happen. Which, no real offense intended to anyone here, we can't.

But I digress.

If JJ3 were to indeed come to fruition, there is something of an argument to be had on the perspective of the game; that is, how you see it, how you play it... well, in layman's terms, where the camera is located in respect to the player. If that isn't disambiguation, I don't know what is.

So yeah.

First person shooter, like the Unreal Tournament series Epic seems to have made a rather healthy living in putting together year after year? It seems fitting enough... character has gun, will travel... and wax anything that gets in the line of fire.
Third person shooter, a la Max Payne? It still offers the opportunity and capability for 3D play, but I imagine it lessens the "impact" of the gameplay just enough so that distraught, uptight housemothers won't come breaking down the door with their shrill cries of "YOUR GAME MADE MY SON BRING AN LFG-2000 TO SCHOOL."
Side-scroller, as JJ3's predecessors have been? There's not really any opportunity for 3D play here, but it's certainly something JJ fans are used to playing. Comfort in stability, or something along those lines.
Did I miss something else here? 2.5-dimensional play, like Starcraft? Or, hey, let's get ridiculous and say one-dimensional gameplay. Nothing more exciting than a string of atoms on a mission to save the universe!