I'm some 4-5 hours in, only got to sink my teeth into the game today and holy shit! It's easily the most fun I've had on my PS4, and that's counting playing Destiny with a good group and experiencing TLOU multiplayer for the first time, both of which I really liked.
The nemesis system is great, hunting down the assholes that killed me or picking the next target out of the list and just hunting him down even without any sort of a grudge formed yet feels amazing.
Right now I'm after Bolg Raid Leader, I ran into him in a stronghold while hunting down some random grunt who got promoted to a captain when he killed me right at the start of the game - and this Bolg guy is a fucking shitbag. He's a monster slayer who hates Caragors (which is part of the reason why he got me, as hunting down the other guy I let some Caragors loose on the stronghold), also a combat master invulnerable to Stealth. But that's just why he's hard, not why he's an asshole.
He's an asshole because when he beat me, he basically said killing me isn't worth dulling his blade and just walked away like I'm nothing. Gonna teach him some manners now that I've got the full intel on him.
Another asshole which I'm sure I'll see again is Gorbag the Wrestler - that guy killed me twice, once through my underestimation of his abilities, and once by just showing up as I was messing around with some uruks. Crashing his feast and making him run away like a scared little girl before I hunted him down and killed him (but no decaptiation) was a highlight of the game for me so far.
I can't believe how smooth and satisfying everything is. And I love the talent tree, tons and tons of really cool abilities that make me anticipate a level-up more than I would have imagined.
I've decided to give Shadow of Mordor a try unless reviews said it was terrible right around this year's E3, but I've never expected it to be this good. What an amazing gem of a game and a pleasant surprise.