I could very almost like Lights(As well as a lot of Ellie Goulding songs). But there are some certain sounds that will just ruin any song for me, and the two sounds that do this most effectively are 1, autotune(Anything with obvious autotune I just cannot listen to), and 2, I don't think there's an official term for it, but when a word or short phrase is repeated over and over again in a short period of time and the ending of each word/phrase is slightly clipped in editing so they can fit more in. I don't know why this bothers me so much, but I just can't stand it, and it happens somewhere around 2:22 and again near the end in Lights. It's almost exclusively a problem in modern songs, because of the computer editing it requires. It's not that I'll objectively call her songs bad, but pet peeves prevent me from enjoying most of them.
To my knowledge this is the only Ellie Goulding song I like:
https://www.youtube.com/watch?v=0Hstt2EG9Us There might be more, but if there are I haven't heard them.
I've noticed something about metal music. Except in some rare cases, the first time you listen to any heavy metal song it sounds super-generic and unmemorable. Case in point, the two you just posted, I listened to them a few minutes ago, and already I cannot remember the tune and barely any of the lyrics. Same goes for the metal songs I like though, so I don't know if those are mediocre or if I just haven't listened to it the necessary five times to pick up any nuances and see if I like them or not...
Also case in point, this song
https://www.youtube.com/watch?v=sZpbCLdg-r8 Not usually my kind of music, and I thought it was pretty mediocre at first(And only listened to it in the first place because I follow MoS), but it's grown on me.