While I like the idea of The Happiest Apocalypse on Earth, this particular Apocalypse World hack, for me, was marred by many design decisions which don't seem to hold up particularly well under scrutiny. Like most other games which run on the Powered by the Apocalypse sytem, HAoE is built around a serious of "moves," mechanical effects (often rolling a pair of d6's) triggered by PC actions, and it's in it's moves that I had the most trouble buying into the game. While HAoE is built on the premise of doing an action-horror game, I was struck by the way that it's moves actually strip away much of the tension one can find in the original Apocalypse World. The roll for aiding or hindering another player, for example, in the original Apocalypse World, on a success, would let you give another PC a bonus or penalty to their own roll. A partial success, however, would put you in a bad spot of some sort as a consequence of helping them. In HAoE, a partial success only reduces the amount by which you change their roll, with consequences only coming back to you on a failure. In looking through the other moves in the game, both in the basic moves available to all players as well as moves available as character advances, I noticed that this design decision was a recurring choice Grey's made throughout the game, often removing the negative consequences of partial successes to instead inflate the value of a full success. For me, this poses two problems to the game's design. Those consequences on a partial are a big part of how PbtA games keep itheir forward momentum, the plot moving forward as new problems or crises spill out of players not getting a full success, which is why other PbtA games tend to limit the number of moves that give you what you most of what you want with no consequence or qualification on a 7-9. But, more importantly, this decision seems to work against the kind of bloody carnage horror most of the game's examples of play imply this game is supposed to be about, with many character actions letting them skate through relatively unscathed.
Moving on to character creation, I feel like the system's a bit more convoluted than it needs to be. Rather than pick a playbook (PbtA's version of classes) or adopt a more open-ended character progression system that some PbtA hacks such as The Warren have adopted, HAoE has players choose and combine three different sets of mini-classes at character creation: personality, background, and whether you are a guest or employee of the park. While I thought having to pick separate personality and background classes was a tolerable if not great design decision, having the option of playing guests struck me as a something that should really have been left as an optional rule for one-shots rather than as part of the main game, as I feel like playing guests in a multi-session campaign will probably force most groups to come up with narrative contrivances as to why you have PCs spending all their time at a theme park where scores of people are murdered on a regular basis without just being an employee. The core set of stats, as well, could have easily been pared down, "Stout" not really doing anything other than offer a slightly modified version of "Be bold and daring" (HAoE's version of keeping your cool, for those familiar with Apocalypse World), a roll attached to the player's Brave stat. It could be argued that Stout narrows the range of player actions that rely on their Brave stat, so it might serve a purpose there, but the wider design of character options seem to make it pretty glaring that Stout doesn't have much use in the design outside of that, with only one other move among several dozen actually making use of stout, as well as a move that let's you "Be bold and daring" for ALL rolls that use Stout.
Continuing to the Gming session, HAoE, like many PbtA games, defines the forces that make up the world through the categories of Dangers. Where the list of GM moves is meant to give the GM a quick set of ideas for what to do when a player misses a roll, gives them a golden opportunity, or just look to the GM to do provide a response to their actions, each Danger category is a set of unique moves which the GM can look to to make a threat or character more distinctive in their behavior. While this section is generally adequate, I do feel like there are parts of the text here that confuse the reader as to what GM moves and Dangers are. There is a recurring move in all the dangers which reads "Stop another Narrator move," which seems to be a Narrator move about not making a Narrator move. As someone who's read A LOT of PbtA games, I THINK I know what those are meant to be saying, but those moves could probably stand to be rewritten to say things like "Rally to oppose the park's weirdness" or "Reign in guests," as these make it more clear that, if you're making a Narrator move SOMETHING should be happening. A narrator move that says nothing happens doesn't give the GM much to work with. The other really glaring issue I see here is the inclusion of "The Big Picture" as a distinct danger. As Grey notes, "The Big Picture" is more about the game's "tone" than it is about a particular problem or character, which might confuse a reader new to the system as to how dangers are meant to be used. Given that many of its moves can be "deployed when there is nothing else to do or when no other dangers are around," I found myself wondering why some of the moves weren't simply folded into the general GM move list, so that what was left could be more narrowly defined as "Madness" or "Affliction", a specific threat that could be answered with player action. While many of it's examples of how to combine these dangers into a session's play are not bad, they tend not be particularly illustrative of good GMing practices for this sort of game either, and I would generally recommend looking to the MCing sections of other similar products such as Monster of the Week for advice on how to do episodic play rather than rely on this book alone.
What does stand out in the GMing section is the collection of short adventure write-ups that offer easy starting points for grasping the feel and world that HAoE is going for, as well as offering, generally, better examples of how to build an adventure for the system than the GMing advice, itself. I would, perhaps, have liked a bit more variety to the adventures on offer--nearly all of them feature bloody carnage filled rising action, climax, and denoument--but they're generally entertaining and will probably appeal to fans of that sort of horror more than myself.