It'd be nice if you could actually pursue deeper relationships with the other characters. Too many of them are game-ending, as soon as D finds out...
Yeah I know the game is Dating My Daughter, but a number of people now have said they like some of the other characters more than D.
I suppose you could peel these off into other games (Dating Jennifer, etc), but at the pace the game updates are going, we might not see such a game until 2019 or later...
My read on Graham and the MC (I'll put this in a spoiler tag just in case):
I may be giving MrDots too much credit here r.e. character motivations, but those are my rationalizations of what we've seen so far.