There is no reason to believe that Gamefreak 'ran out of ideas'. I think that they just wanted to start completely fresh, possibly making original remakes of pokemon that you might have seen before, but in Isshu style. The creators wanted us to think that none of the other regions ever existed. So saying stuff like, "ohh Mamanbo looks like Luvdisc, cause it's a heart disc" its kind of wrong, because from the stance of this Generation, no other pokemon have existed before.
And to be quite honest, I love some of the concepts of pokemon I see in this Gen. My favourite to be honest.