Best: New combat, quests, books and clothing that give boosts, much more progressive skills(the RNG of finding books for progression was a less likeable feature), love the big new content like gun attachment and vehicles but never got the chance to test it.
Worst: Dying A LOT: feral sleepers, wolves and dog horde spawns should be linked to game-stage(which it isn't). First death was to a horde that spawned at dusk and tracked me down possibly through my noise or campfire. Second death was to 3 ferals in a basement. Third was an infection from a vulture causing extremely bad max stamina, got mauled by a passing wolf.(not a lucky man today)
RANT WARNING
Biggest issue is with soldier ferals: One spawned on the top floor in a barn as I was doing a quest to retrieve something: a dog horde also spawned, which I could shoot arrows at with the soldier which fell to the bottom floor since there was a narrow beam it had to walk across. I managed to dispatch the dogs and a few passing zeds but the soldier just wouldn't die. I got impatient and tried to spike him but his "smart zombie AI avoided the spikes and I ran out of stamina(by extension, out of life) trying to play ring-around-the-spikepit. This kind of enemy should have ZERO chance of being encountered before Day 14, let alone on Day 5.
Did some testing: they can take, separately or combined, more than 120 bullets, more than 80 arrows, tons of shotgun shells and slugs. 2 minutes or so of sledgehammer whacking and not go down. It appears to be protected HEAVILY by its military armour which protects it from physical damage but: it can go down in 2 explosive bolts, 3 to 4 pipe bombs and, VERY surprisingly, less than a minute of getting whacked by a TORCH.