Dark Souls 2 is a reasonably successful experience on its own terms, but stumbles and sometimes outright fails for a variety of reasons when examined closely.
40-50 hours into Dark Souls 2 I came to the conclusion I just wasn't enjoying myself. What was different? Something had to be, after all, I eventually became used to Dark Souls and learned to greatly appreciate it for what it was. I still believe DkS achieves masterfully what it sets out to do and to those with the right mindset it is an engrossing experience.
If Dark Souls ever was "fun", that "fun" has been carefully syphoned from its sequel leaving greater frustration than ever before. It seems obvious to me that the changes in the dev staff have displaced the careful design present in DkS, because its sequel is full of issues. I'm simply not enjoying it as much. Don't play it solo, play it online and request help wherever possible, is my recommendation. And use a character that has good magic and / or a decent bow. Melee characters are just not fun this time.
Combat suffers due to less accurate controls (I'm using the same controller), finickier parrying, unpredictable back-stabbing (when I managed to, I was never once standing "at the back" of an enemy, only off the side a little), and worse of all: unreliable invincibility frame placement during rolls. Agility changes this, but it never becomes entirely "learnable". Weapon degradation is too rapid. The reason for joining covenants is never explained, and leaving them has no penalty any more.
The considered one-on-one battles of Dark Souls were tense and compelling, but much of DkS2 has the player face multiple enemies at once. In fact enemy placement is sometimes a total clusterfuck and tends towards unreasonable. The Black Gulch must surely be a level design nadir for From Software. Really, F*CK the Black Gulch: Hundreds of poison spitters and instant-death submerged trap hand mouth things that shields do NOT protect you from. The boss is ridiculous as well, and ALWAYS locks on to you. (Many bosses conform to a formula: oversized humanoid with oversized weapon, a few similar melee attacks, and a way to catch you when you're behind them.) Soldier's Rest is a mess: teleport to it, exit the building housing the bonfire, and then THREE old ironclads are on your tail within moments, plus a few undead soldiers. The run from Huntsman's Copse -> Bridge Overview to the Undead Purgatory is endlessly frustrating, punctuated by those "dark staff" monsters that kill in seconds. Many bosses, like the Pursuer, just take far, far too long to kill even with upgraded weapons. I'm struggling to think of occasions in DkS where the game felt as unfair, slow, or tedious. Maybe, maybe going through the Undead Burg the first hours, but that is rather due to player inexperience, not poor design.
Level design is haphazard, sometimes lazy and boring, other times inspired. But never coherent. I'd love to see the invisible elevator that takes one from Earthen Peak to Iron Keep... from the OUTSIDE. After killing the four boss souls (why?) ... some stones are removed from an arbitrary invisible wall to allow progress. The Tower Of Flame is essentially a series of linear corridors with a few battles and a single branching point. There's much more, but the game is littered with these issues.
Useful items are scarce for a great deal of the game. Titanite is given out so frugally, and cannot be bought from an "unlimited" source until very far into the game, meaning upgrades must be chosen with extra care. It's quite possible to be stuck with a character that is otherwise well built, but has rubbish weapons that cannot be upgraded due to a lack of souls and titanite. Oh and due to the monster spawn limit, farming isn't an option. I faced the Iron Keep with weapons that just weren't quite good enough and I'd spent all the souls and Titanite I could. An ARBITRARY limit on purchasable Titanite shards is then lifted after completing the Iron Keep. WHY ?? WHY??? Another boneheaded decision!
Most NPCs have no reason to exist other than to provide items, complain to the player, and then sit in Majula and do bugger all for the rest of the game. Why must I talk to a specific NPC to level up? This is one of the few hold-overs from Demon's Souls that seems pointless. And why am I in Drangleic in the first place? This is never clearly explained, I'm just here to ... kill four bosses? Why? DkS1 made it clear the player is there to succeed Gwyn and ignite the first flame.
Not a successful sequel, Dark Souls 2 strikes me as ill-conceived fan-fiction. Those that remember Ultima 9 know how that plays out. This game is not recommended unless you can forgive all these issues.
I also recommend watching Matthewmatosis' video:
Edit: Operating very much at the extreme end of the critical scale Michael Thompson's particularly damning article thrashes the game. While I would argue some measure of suspending disbelief is always necessary when gaming, in this case, Dark Souls 2 is simply not worth it. But Thompson comes across as though gaming - for him - is a penance, so it's difficult to resonate with his thoughts.