Currently in NG+ at the non-poison swamp letting people invade me for some good ol' 1v1 no-heal duels. I've invaded as well but I'll focus on people who invade me because they're actually looking for it.
1. People really like their R1 spam and that tends to get them killed. So far, Invaders seem to think it's Dark Souls 1 pvp all over again with infinite staggering and it's fun to watch them realize that it doesn't work like that.
2. The big game-changer for me are weapon arts. I didn't find many uses for them in pve but hoo-boy are some of them pretty powerful in pvp. I use the Dark Sword's weapon art all the time; even just using the stomp and not swinging gets people to start rolling and it's VERY easy to time your hits for the end of rolls in this game (or at least easier than previous entries). The weapon art move itself gives you hyper armor since it shares the stomp with greatswords and ultra greatswords which people luckily don't realize so they try and R1 me out of it, only to take 400 damage to the face.
3. I feel like every third person I fight is using the uchigatana.
4. Backstab fishing has not returned and parrying is so finicky and risky. I think I've been parried once and the other person was as surprised as I was that they didn't follow it up.
I'm definitely new to the pvp side of Dark Souls games but it's really fun this time around and when I do run into someone who knows what they're doing, I get destroyed.