Single player, by 
It’s nice to see a level that knows so clearly what it wants to focus on: in this case, gravity flipping. Once the player gets out of the outdoor tree area, they embark on a gravity flipping adventure, navigating the same large space from two different perspectives in search of a trigger crate to remove a column of buttstomp scenery blocks. (Why the lock block graphic was unavailable is unclear.) It’s complex and puts a lot of faith in the player’s navigation skills, though there are a few places where the layout doesn’t seem to fully anticipate how much wandering the player might do… the top left has a rogue sucker tube in the ceiling, which is bad if your gravity is flipped, and it takes too long to flip your gravity upwards if you flipped it back downwards at the wrong spot.
Once you get past this first big section, the level becomes more linear, although a few more trigger crates do turn up, and likewise another (much shorter) gravity flip sequence. I almost wonder if the level’s order of events might have been better reversed, so the player could encounter the simpler stuff in the latter half of the level first, learning the level’s vocabulary in a more linear environment, before having to navigate the more complicated puzzle at the start. A similar questionable order of presentation occurs with the beer pickups, which temporarily reverse the player’s controls. They’re a neat idea and manage to avoid being used too frequently, but the very first one is directly above a pit of spikes. A softer introduction in a no-danger environment would probably have been better.
The last main non-vanilla piece of the level, besides the gravity and the beer, are snowflake pickups, which serve as a basic collect-‘em-all goal and use nice seasonally appropriate graphics. It’s a little confusing having both snowflakes and coins in the same level, but otherwise these are a fun addition to the JJ2 formula, and it’s good that the HUD lets you know how close you are to completion. They’re mostly placed fairly, except for a few in a vertical area that I tended to shoot down while aiming at ravens, which wouldn’t have been so bad if my gravity hadn’t been reversed at the time. The pickup sound effect kept making me think there were demon enemies nearby, though. The intro level also does good work on the snowflake front, showing the player (in a low-stress environment) that there’s no gameplay effect to collecting them, only some green HUD text and a sense of completion.
I haven’t mentioned the intro level before but yeah, this isn’t actually a single level, there’s also an intro and a boss and an outro and a silly bonus level. They all do their respective jobs admirably well and so it’s harder to find things to say about them, but here are some random thoughts: Drawing an entire alternate graphics set for an existing JJ2 boss is impressively ambitious. The steam events in the intro were kind of annoying. The sucker-tube-based dialogue (a holdover from Faded Story) still feels weird, especially immediately after a clearly scripted explosion sequence. The sciency base area from the intro/outro is a bit quaint but quite nicely put together. The bonus level is good and it makes sense it’s not trying to develop itself into a full map with a detailed layout and stuff.
Graphically everything in this upload is quite solid, as you’d expect from someone with a background in multiplayer levels. The palette and tileset choice are distinctive, leading to memorability, and everything has enough detail to be attractive but not overwhelming. A few of the spikes do cross the line into nearly invisible, though, but mostly it’s hard to know what to say about the visuals other than that they’re good. Same goes for some of the more linear gameplay sections I didn’t really dwell on above… yeah, they work fine, there’s a good mix of enemies and layout styles, platforming and vines and open spaces and caves and all that stuff.
