I think it depends on the overall quality of the game produced.
There's a right way and a wrong way to borrow mechanics from other games. Take DI's predecessors in this past month, Bayonetta and Darksiders. Bayonetta was largely seen as taking a lot from Devil May Cry, and Darksiders was seen to have "ripped off" Legend of Zelda/God of War (especially Zelda - but hey, Zelda for Xbox/PS3... I'll take it!) Anyway, Bayonetta was forgiven for firstly, having DMC's creator at its helm, and secondly, having fantastic gameplay, being able to take the DMC formula and add uniqueness to it. Likewise, while there was less original about Darksiders than Bayonetta, the combination of mechanics swiped from Zelda and God of War were brought together in a way that produced a very enjoyable final product. These games borrowed in the "right" way and were rewarded for it with decently high reviews and sales.
The biggest culprits of games that do it the "wrong" way that I can think of are movie tie-in games and the numerous Pokemon copies on the market. With the movie tie-ins... well, some movies just should not be made into games in the first place, but don't make it a freaking copy of some other popular game. With the Pokemon clones, when what you are is so obvious that you have your various creatures on your box art and your name even looks like a copy of the name of the game you're cloning, it shows that you know less about designing games than deftly maneuvering around copyright law. They have only been lucky that their game hasn't sold well or Nintendo would have sued them into the unemployment line within a few weeks of the game's release.
So I say, originality should still be a factor, but if the game is still quite well made and especially if it has made improvements or fixed errors in the game mechanic it's borrowing, the game shouldn't be punished for it. In fact, I would welcome such moves if they do make improvements to them. Then perhaps the original developers can learn from those games when developing sequels to the original games.