A lot of example levels for JJ2+, demonstrating how to use various new features. The suggested starting place is plusMenu.j2l, which serves as a hub for all the other example levels. This is strictly an optional download, but it's harder to get a sense of how awesome JJ2+ is without it, so click away! Tetris, illustrations of new online gamemodes, multiplayer levels, epic single player experiences, timers, and more await you.
Speaking as a longtime Jazz2Online member and even longer Jazz Jackrabbit 2 player, I can say with confidence that the things Plus does with the program are simply mindblowing. I never thought I'd see so many different possibilities or different things it would let you do with the game. I would highly recommend its download, whether you're a prospective Jazzer like me, or just someone new to the game. You won't be disappointed either way.
-PT32