First off, this post will contain some spoilers about the nature of the adventure, but I'll try to avoid spoiling the adventure itself. But I wanted to talk with what problems I view the module as having, and what uses I view it as having.
So the adventure itself is a total screw job to whomever plays in it. This is to be expected from a LotFP adventure and being surprised by this is like being surprised that your banana split contains ice cream as well as bananas.
This can be an issue in this case though. Many of the encounters within have really inescapable outcomes. There can be a handful of outcomes, but far less "lateral thinking" solutions seem available. This isn't to say it is inconsistent. It is a fairly logical (if you can say that about something beyond human understanding) way the area would behave. It isn't meant for adventurers to romp around through, it is just a powerful artifact they can stumble upon.
That is the problem as well though, it isn't meant for adventurers. It is an interesting and fantastical location, but I wouldn't consider it a good adventure location, it is a horror location. This can pose a problem is a group is only going to investigate the monolith for metagame reasons. I don't mean that as a bad thing, sometimes you are cognisant of the fact that there is only four hours every other week to play and you just go towards the nearest adventure location. Such a group will feel sorely cheated that the other end of the implied bargain wasn't kept to. "We bit the adventure hook because we didn't want to waste time dithering, but you just laid out a poison pill? Not cool".
That said I see it as having fantastic use, but it needs one or two minor tweaks. In a sandbox game it can be used as a perfect example of why not to investigate every damn oddball thing your PC hears about. "Oh there is a radioactive city over there? Maybe I shouldn't investigate it since nothing about radioactive city sounds pleasant and I shouldn't assume that everything is set up to be a fun adventure, and in fact some things are just deadly". What the monolith beyond space and time really needs I think, is a Zeke equivalent (from Death Frost Doom, another LotFP module that is held in near universal high regard) to warn the PC's that there is nothing but doom ahead. I am reminded of Liam the Wayfarer (ref. Jack Vance "The Dying Earth") who when approaching Chun the unavoidable is warned by an old man showing many a previous victim. In neither "Liam the wayfarer" nor "Death Frost Doom" nor "The colour out of space" nor any other horror cliché using this trope, is any heed ever paid to these old men warning of your unavoidable doom. That isn't the point, the point is the warning is retroactively acknowledged. Cryptic and unintelligible babble has meaning thrust upon it after the fact, and people are probably a little more happy with the screw job.
So if you just have an "adventure of the week" where the GM gives the players an adventure to play, The Monolith seems like a dick move and generally wasting a large and valuable chunk of your friends free time. If it is a more player driven or sandbox game where players choose to explore the monolith, for no reason other than curiosity? Well, the old saying "curiosity killed the cat" exists for a reason.
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