Honestly if there was an airtight formula, we’d probably use it and be millionaires! But there are some trends - scifi and historical fiction have been mentioned before as genres that have undersold, though I don’t know how up to date that is. There are some straw polls about favourite and underrated games, and more discussion of underrated games here (though I’d take some of the assessments of underrated games with a pinch of salt as some of them mentioned are very popular indeed!)
It’s tricky to assess using forum commentary, because broadly the forum is a minority of the Choice of Games and Hosted Games players, and it’s tempting to pay a lot of attention to the extremely high selling/high discussion outliers. There’s some discussion here about revenue numbers, but again there are some very high numbers floating around there which shouldn’t be considered commonplace!
All of which to say, it’s not easy to judge what will or won’t be wildly successful, and we’re at the mercy of app store algorithms as well. The Great Tournament is free to complete though, no? That will definitely impact download numbers.