Released in 2003, the design has improved from Crash of Gobo III. There are still recolored graphics, but there's noticeably original enemies like the noid (giving me Spax 3 flashbacks) and the tank robot replacement which is an electric orb. There are a full 16 levels this time with more fair difficulty, though there are some cheap jumps. The levels are less labyrinthine than keen 2, but turning off the lights makes you unable to see the keys and the art of the planets in the planet destructors.
An elephant in the room I haven't mentioned is that Gobo III is the yorps' home planet in this series. Was Ceilick retconning, or did he really not realize that yorps and gargs are Martian NATIVES, not immigrants? It's the same awkward retcon feeling I got from playing the Norp the Yorp series, and at least those addressed that Spot got a legal name change.
Two levels are exactly identical. I don't know if Ceilick copy and pasted out of laziness, or there's some long lost level we'll never play because he accidentally overwrote one of them.
There's a sort of odd charm in the ending in that it is (spoilers) almost exactly the same as Keen 2's ending. The "eat a vitamin-fortified bowl of sugar stoopies before you go" line is untouched, reused word for word. It doesn't come off as lazy; there's a simple honesty for the fact it didn't need to be changed. (/spoilers)
Better than Gobo III, but I still used godmode to cheese some of the levels, which is a sign that they're not fun to try to accomplish (I never use godmode in Keen 3, which is harder than this, so there's some intangible element that makes some challenges more fun than others).
It's kinda boring at times, but it has a ship shaped like a yorp. Next up is Tribulation of the Yorps on Yorpicon IV (do these guys have 3 home planets now?)
(Note: You need to extract the mod files over a fresh copy of Commander Keen 2 in order to play.)