Normally I wouldn't necessarily recommend Game Grumps to all Rifftrax fans (though maybe to Rifftrax fans who are already into video games). Normally they just talk about whatever while playing video games and only occasionally break out into Rifftrax style riffing.
But their Lets Play of Doki Doki Literature Club is basically a fully improvised Rifftrax style riff and its pretty hilarious. They layer on a lot of running gags. I think its some of their best work. So I'm recommending it here. You can find it on YouTube. Sorry I can't post a link. I'm at work so I can't look it up at the moment. Just type "game grumps doki doki" in the search.
And Doki Doki is a pretty interesting game in its own right. I won't spoil it and you shouldn't either but it has a little more going on than it first seems. But even if it didn't, Danny and Arin's riffing makes it so entertaining I almost wish it was just that.They layer on a lot of running gags.
And if you've played the game, Danny is going in completely blind and Arin only knows a little bit about the twist. So you can have fun watching them react.