GH was a decent franchise, but Activision milked it to death. After a while there was no innovation to be had. They continue to try, but I see no difference in sequels -- unlike the radical differences inherent in every release for the first three (considering the third was the first game made by Activision).
Now with everyone already owning their fake plastic instruments and playing the songs they want (or making customs if they cannot find them), Activision should have realized the waning interest in the franchise a while ago.
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"As below, so above and beyond I imagine / Drawn beyond the lines of reason / Push the envelope / Watch it bend..."