Anecdotal, but my teenage nephew (he's around 14) was super excited about Forces but didn't give a fuck about Mania when both games were announced. I think Forces will do as well as Generations, maybe slightly better - but I think Mania will surprise the hell out of them, smashing their expectations, getting rave reviews and essentially becoming a critical darling - because from the previews it pretty much already is one. Just want Mania to sell well enough to secure a Mania 2 - though I think that's extremely probable. It still has more positive coverage than Forces overall and will likely destroy Forces in reviews. In defence of Forces however, the previews are only really previewing barely any of the game - the final product could still be decent.