I'm thinking of playing the game again on a harder difficulty level (I don't remember what or how many levels there are, but I imagine I played it on the default/normal difficulty). I'm aware that one aspect of the next difficulty level up is that meditation doesn't result in healing, but is there anything else I ought to be aware of?
At the higher difficulty settings the witcher resources (potions, oils, etc) become a lot more important. However even on death march the game might start feeling too easy after level 15 or so if you are using all those resources, have a decent build, keep your gear updated, etc. You might want to turn on enemy level scaling or tweak your build & play style to make things more interesting. For example I'm at level 85 and just finished the base game on NG+ and really for the entire NG+ playthrough I haven't bothered with oils or potions except on bosses and large groups, and that's even being down two skill slots because I didn't unlock everything before starting NG+ (be warned if you intend to do NG+).