The official PS+ quality guarantee that is Metacritic makes it a fact. It's not highly controversial even if we take Metacritic out of the equation either, you know. Just PS3 and Vita games was the highlight of the service at least in Europe.
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http://en.wikipedia.org/wiki/List_of_Instant_Game_Collection_games_(PAL_region)
There's no "nosedive" of quality anywhere, it's getting games pretty on par with 2013.