Board Thread:Dark Souls II/@comment-6132984-20140420185756/@comment-16047389-20140422174130

Enemies get stronger in NG+ (I believe it is double damage and double health), new enemies appear, some enemies are converted into empowered red phantoms, and bosses drop their souls and new items as well.

Now as for your question "Is new game plus that much harder?". Honestly, I'm having an easier time breezing through NG+ than I did on NG. Arguably this is because I now have my core items, upgrades, and spells from NG. I was hoping that some of the bosses would gain new movesets or new mechanics, but the closest they've added to make bosses harder is the inclusion of additional enemies that appear during some of the fights (i.e. Flexile Sentry and Lost Sinner).