I like the fact that it gives him more of a reason to fight, motivation. (Although I think that sticks better with Bruce's character). And that it sort of keeps things in perspective for him in the sense that it makes him realize that as powerful as he is, he can't do/control everything.
But it sucks to see a person, especially with the powers and characteristics that he has to be so lonely. That's one of the nice things to me about L&C, he always has his parents to call back on whenever he's feeling down or he has a tough decision.
I'm not sure. I liked that they let the Kents live in the John Byrne reboot 20 years ago, and they are still around. Just having Jonathan Kent die in the films, it contained the message about things that are beyond Clark's power (though he would break that rule by time-travelling to save Lois in the first film.) I wondered whether Martha would pass away in SR, but maybe that's for the next film.