Single player, by 
The trap that scripting springs on unsuspecting level makers is suddenly there's no reason to take shortcuts, other than, well, they're easier. The Medivo level pits you against enemies that have been given boss health bars, but there's nothing to ensure you actually fight them instead of skipping them. Text strings politely ask you to go back if you didn't fight them, but that's all. In the Psych level, an invisible coin warp takes you to a TNT pickup and another warp back, instead of a script giving you the TNT ammo directly if you have enough coins. If the levels had no scripts at all, these would be understandable compromises, but because other things are scripted, suddenly these are points worthy of criticism.
(Similar issues apply to editing tile(set)s—suddenly every drawing made in history is theoretically available, so why settle for a tile that's close enough?)
Focusing on what the levels do do, though, rather than what they don't: this is pretty all right. Lots of pickups, including the traditional JJ2 thing where individual levels focus on individual ammo types. Trigger crates that aren't too far from their respective (clearly marked) trigger scenery blocks and sometimes do interesting things like sit on top of spikes. Level layouts that go in all directions, not just right, and feature tileset-specific obstacles. For all that the bosses are the most memorable parts of this pack, the levels aren't just window dressing, they're worthwhile (if not amazing) in their own right. Generally a pretty good time, though everything (eyecandy, layout, scripting) could take a bit more polishing.
