This review contains mild spoilers
As with many modules, there is both good and bad to be found here, although in this particular case, the good is neither so good, nor the bad so bad to tip the scales significantly toward one extreme or another. Instead, what we have is an interesting and promising, if also flawed scenario.
The campaign provides good framework and backstory for a post-apocalyptic Cthulhu mythos game, there is potential for outstanding individual scenes, and with assistance from the module, a commited keeper can likely create an atmosphere of dread and wonder within the context of the tale. The writer (and indeed the module is quite well written as well as asthetically well-designed) provides ample opportunity for interesting imagery to be evoked. Still, depending on one's group of players, I have at least some doubts about how effective a botanical apocalypse will be in terms of evoking horror. The deadly flowers are an odd choice of plague, and as my gaming group has made a habit of mocking the much-maligned film "The Happening" (also centered around plants gone bad), I'm at least a bit concerned that the flowers may produce some eye rolls rather than chills. At least that's me. To be fair, your results may vary.
Setting aside this concern, the first and third acts are well structured, and provide several interesting moments (a first glimpse of a monster which-should-not-be rising from the ocean, an exploration of a town become a flowery tomb, the discovery of a ancient and mathematically impossible game of mythos chess) and the ending is especially potent in this reviewer's opinion. My main problem, and that which keeps this review at three rather than 4 stars, is the second act. This act (invloving the Great Race and an odd side story involving psychic time travel) momentarily causes the wheels of a strong story to nearly fall off. I begrudgingly admit that this portion is appropriate for a tale of the Great Race, but feel their inclusion would have been better left by the wayside. The section (which depends upon PC collusion with the GM) feels gimmicky and forced. It doesn't particuarly add much to the story other than provided the players a directive at its conclusion which moves their progress forward. I'm sure a crafty keeper can keep things moving towards the final events without running this portion as written. I find it a striking change in game tone, and an odd and eccentric chapter at odds with the rest of the scenario.
This scenario is ultimately worth a look as a demonstration of how an Apocalypse Machine campaign could go, but could use some tweaking. I will say that I look forward to further installments as the scanario does have potential that was almost, but not quite realized.
[3 of 5 Stars!]