There are a couple of ways we can take this question.

If we’re talking about games that are bad on purpose, then it’s basically a tie between The Extraordinary Adventures of Baron Munchausen and Wisher, Theurgist, Fatalist (warning: direct PDF link). The former is a game of competitive bullshitting that’s written entirely in character as the good Baron, and as such tends to ramble, pontificate, and go off on long tangents about nothing in particular - and in the process manages to serve as an excellent primer in the kind of narration that’s required to play. The latter is a deliberate parody of independently published tabletop RPGs that are so high concept they’re essentially unplayable, and while it does an admirable job of being exactly that, it also has some fascinating ideas about the division of responsibilities at the table, a topic I touch on in a previous post.

If we’re talking about games that are bad by accident, I’d have to give it to Continuum. In a nutshell, you play as members of a trans-temporal police organisation, preventing malicious vandalism of history and prepare humanity for the next stage of its social evolution. So far, so good - but then you get to how time travel actually works.

How time travel works in Continuum is like a cross between Back to the Future and Bill and Ted’s Excellent Adventure, except played utterly straight. You can do pretty much whatever you want, declaring that your future self shows up to help you, or that your enemy’s trap is actually a double-bluff that you yourself will have set up in the future to trick them into believing they’d trapped you, potentially turning every conflict into an impossible Calvinball-esque snarl of “ah, but I knew that you knew that I knew that you knew that…”.

The price is that you actually have to play out that setup later, which your enemies can potentially interfere with in the same way that you did, and you can’t even kill them without causing a paradox due to all the stuff they already will have done. (Well, you can, but then you have to arrange for an actor to impersonate them in order to keep your own timeline intact.)

Like, there’s a formal “time combat” system for this and everything. It’s wonderfully weird, but I have literally never heard of anyone, anywhere, in the entirety of the nearly twenty years since the game’s initial publication who’s managed to successfully play it as written.