It really depends. Dick Grayson was changed from your standard white boy to Romani in the '90s and that was a really smart move by Devin K. Grayson, and I still like to think that little alteration is still canon because it really did add to Dick's character.
On the other hand, there's Wally West. Wally was, like Dick, your standard white boy, but New 52 (and probably the TV show The Flash) changed Wally's race to black. That was a really stupid move. Most of Wally's character development in the comics hinged on his being a conservative white kid. Changing his race erases all that character development and adds nothing.
Ordinarily I'm all for white people getting swapped out for minorities, though. But people like Wally should stay white.
Re: comic book movies in general, I honestly don't see anything wrong with this wave of comic movies. I see it as its own subgenre, like westerns or romantic comedies. I know the wave probably won't last long (hopefully through 2020 to get to those DC films), but as a comic fan, I quite enjoy it.
Just as an FYI to some people in the thread: the movies really only loosely follow their comic counterparts (and some are nowhere near their comic counterparts like The Dark Knight). For the most part, the films are original stories. I'd also like to point out the companies are putting out very different films tonally. Man of Steel and Iron Man 3 aren't exactly alike.