That link was for a thread about bad old games. If you take all the games on GOG (see here), the title goes to Paranautical Activity Deluxe Atonement Edition, or to Dark Matter if you also consider removed games.

P.S. If you allow DLC, there are even "worse" ones (see here)

Oh, overlooked that tiny detail... Thanks for the correction.

My pleasure. Thanks for endorsement.

I agree that Rebel Assault is a pretty bad game. But it's still a milestone of gaming history - I just looked awesome and many people bought am expensive CD-ROM drive at the time just to be able to play it.
Of course nowadays the gameplay still sucks, and the visuals are a little less overwhelming. :-) But back then it was a "cinematic experience", that even if it was crap as a game.

Arguably the worst game is Grimm.

There is no argument about it being worst. The argument is whether it's a game.

One man's garbage is another man's treasure.
;)

I've always been curious about that one. I got pretty bad reviews, but might be interesting from an artistic point of view. But I've never dared to buy it...

So much for their PR BS about them carefully selecting their games to ensure that their customers have a boutique experience and that the games get the exposure they deserve blah blah... I hadn't seen that they had released that. That paranautical thing looks atrocious.