Yes Mario Galaxy is the least creative game of this generation.
I wasn't the biggest fan of Mario Galaxy, but it was alright. Japan is just extremely trend-based, and it's something you see reflected a lot in their media (such as anime, where it's really pronounced). Once something becomes popular, suddenly everyone has to follow that trend until the next trend is found, and it really stifles their creative output.
What you just said also describes the Western industry as well. Just look at the large amount of FPS that have been released on the HD systems where most of them are basically clones of each other. Not to mention the yearly sports and music games that are no different from each other as well. Of course the music genre is basically dead now because of how badly it was rehashed so I guess that doesn't count anymore.
Plus most of the critically acclaimed Western series from this gen have already had at least 3 sequels made for them by now that are basically the same damn with minor improvments. Which is no different from how a lot of the Japanese companies work as well.
Not to mention I wouldn't criticize Japanese media that badly when America's number one most watched TV network is CBS, where over 80% of all it's shows are nothing but sh!tty CSI rehashes and the other 20% are generic comedies that use the same damn jokes and cliches that have been around for the last 40 years.
Not to mention look at the overwelming amount of remakes and sequels that Hollywood has made in the last 10 years, as well as the amount of remakes and sequels that are currently planned on being made. Hell in the last decade, only two, I repeat two of the 30 highest grossing films the last decade were from original movies not based on an existing franchise or just an aptaption of somthing else.
http://www.slashfilm.com/only-two-of-the-top-30-grossing-films-of-this-decade-are-original/So I wouldn't single out Japan when the Western media is just as bad when it comes to trends and following what's popular.