I think people complain about God of War clones for two reasons: Firstly, every single action game made by western developers is a God of War clone. Heavenly sword is the only one that broke the pattern, and look how well that turned out. And secondly, and most importantly, God of War's gameplay is mediocre at best. Bayonetta is a Devil May Cry clone with a bullet time gimmick thrown in and people are declaring it game of the year, game of the generation, game of the forever. Clearly, cloning something is not a big issue when the game you are cloning is actually great.
That being said, I am looking forward to renting this someday. And Dante's Inferno. And Wolverine.
Re: Metroidvania. Most people don't complain about Iga's Metroid clones because they are essentially the only team keeping that subgenre alive. Who else is making Metroid games? There was that one Spider-Man game that was kinda like Metroid, and Shadow Complex. That's about it.