Yes, the arcade jumping in Pagan was awesome. The QTE combat in the Witcher 2 was great. The MMO grinding in Amalur was highly praised, etc. That's why. Certain blends just don't work well together.
Sometimes it does though, so I'm a bigger fan of focused but can live with some attempts at blends.
I have only played The Witcher, so can't comment on the others, but as I see it, that's not a genre mix, but more of a console mix and bad design. It's not a mix of FPS and RPG like Deux Ex, which I see no wrong in in itself. Of course, there may be some shitty elements to it, or if you dislike FPS then you're likely to dislike the game, but that's not because of mixing, you just don't like any FPS then probably.