The 'Jazz Jackrabbit website' has been down since the start of this millennia. This site and their community is doing more awesome than ever these past few years. JJ2+ skyrocketed the amount of fixes and features (with probably the biggest update still on it's way), and a decent amount of quality downloads released. Currently, the latest downloads list has indeed some unsupported ratings that should either be removed or adjusted, but that's by no means a representation of the amount and overall quality of newer downloads.

It's only natural that less levels and tilesets are being made while the game ages. JJ2's community is doing surprisingly well considering it's a 1998 game.