Honestly, I think the best thing that can be done is for the first episode to be released, and for it to be very, very good. Once people have their hands on it, they can then make an educated statement about whether the game (or the point-and-click adventure genre) is any good.
It's pretty natural for people to have a negative or pessimistic view of something of which they have only seen a teaser, like in the case of BTTF:TG. The proof is in the pudding, as the saying goes.
I think the game will speak for itself once it is released.