I like YA paranormal, and I did find them entertaining. They might not be great works of capital L Literature, but as long as you go in with that understanding, I think it's worth checking them out.
I like The Mortal Instruments series, but I think it could have been a triology...it is starting to feel really drawn out. I think I liked the Infernal Devices series more.
I read the first 3. Just found out there's a 6th coming out! But I feel like the first 3 were enough. I do think it was a good series and I would recommend the first three at least.
I found the first book to be just meh and I won't be reading the rest. But I also don't care for the author as she's plagiarized in the past and her published series is just a rehashing of her HP fanfics much like 50 Shades.