Half-Earth socialism is a pretty good game and presents the challenge of fixing climate change with pretty realistic difficulty.

Positives about the game in my opinion are the challenging difficulty and the mostly good job it does for lining up with climate models. There are of course some inaccuracies but to manage essentially sketch out a semi realistic climate model in a game that can be played on a website is fairly impressive and ultimately does a good job of conveying the complexity and challenge of the climate crisis from as much as I know as an oceanography student for what that's worth.
I also like the art style a lot it and it might seem a bit jarring or deep fried to some but I think the visual design does a good job accompanying the themes and intents of the rest of the game.
You're also presented with quite a few different sociopolitical options to try and put forward and develop a solution however this is where it starts to fall a little.

A lot of the negatives I see about it either boil down to advertising the book, political bias or difficulty.
I haven't read the book much so i can't really comment on that but the political bias it present is fairly strong as whilst you have plenty of options to choose there is a fairly limited window on which ones are successful. But, I also think there is an huge overreaction at the moment to any inkling of political bias in games which in my opinion is detrimental to the industry and will only limit future development and creation of amazing games.
As for the inaccuracy of the bias the game presents a very radical path to find a solution and in my opinion maybe a little too strong and does slightly over target ideas like anti nuclear but honestly nothing to get upset about and if the solution to the climate crisis would be so amicable and agreeable then we wouldn't be here.
My biggest gripe for realism is that it doesn't really factor in international cultural differences much at all and tries to cover it all over with the premise of a complete global socialist reform.
And as for the difficulty the same can be said about that it is not a simple problem and maybe the most overall complicated one mankind has faced so far and if it was easy well again we wouldn't be here.

Final thoughts: Half-Earth Socialism maybe part of advertising for a radical book it maybe an attempt at further reach for it's ideas in a new medium but at the end of the day in my opinion it is a fun game, an engaging challenge and a pretty realistic simulation of solving the climate crisis.