Alrighty... I'm a new player, so perhaps I can offer some insights, at least from my perspective. I intend for any criticisms I offer as constructive, not outright bitching.
Firstly, player retention involves a combination of expectation, delivery, and figuring out the right combination of challenge to keep the game intriguing without being either dull or impossible. I suspect we could all agree on this.
So... expectation: This game attracted me through its promise of a deep set of mechanics. Everything from the professional to the active skills offers a promise of a deep set of mechanics that I can explore. Where we already have plenty of RPGs from which to choose, finding something to differentiate your RPG from any others strikes me as important... and this game attracted me via its promise for depth.
But... can you explore those deep mechanics? You get a single character per account with which to explore the deep set of mechanics this game has to offer, with no reasonable way to shift from one build to another. This breaks expectations: you'd expect a game with deep mechanics to offer some means by which one may explore those mechanics without completely nuking a character to do so... unless... all characters are extremely mortal anyway (e.g. eventually even a successful character ages out), where the accumulation of gear/skills/attributes/whatever isn't such a chore that one can't accomplish their build goals with a reasonable amount of effort, meaning you just push your character as far as it can go until its inevitable demise, then explore something else... kind of like a hybrid rogue-like game. Hybrid, because your character doesn't perma-die when killed in combat or the like, but rogue-like in that, eventually, it will age out.
But, from everything I've read so far, people invest effort acquiring whatever their character gains, and would be loath to toss away that effort to explore something else... yet that's you're only alternative. So that's a put-off.
This said, it takes very little time to get to 100 in most of the skills, from what I can tell. I don't know how I feel about that. On the one hand, that plays into the whole 'explore the mechanics' thing I mentioned earlier; don't like where you went? Delete the character and try something else... who cares, you can just level up what you want in a few hours. Except all the gold, etc. that you spent effort on evaporates. But then if it didn't matter, I wouldn't care, right? I haven't played long enough to know for myself how attached I'd get to my acquisitions, so I can't say, but it's something that makes me wonder. And it will make other new players wonder as well.
But, on the other hand, in some ways it makes the game too easy. You don't feel as invested in the character. I guess that's the thing for me... I'd like to feel invested in the character, but I fear doing so sacrifices an ability to explore what this game offers. That's... not great.
I very much enjoy the directional blocking and directional attacking in melee fighting. That's a delightful system. It offers a sense of accomplishment that goes beyond button-smashing, when you read your adversary's tell to work out the correct block, or maybe parry into a riposte. I do enjoy the possibility that a less-skilled player with better gear could be undermined by a skilled player with lesser gear. And I'm intrigued about how difficult this mechanic becomes in the heat of battle, as you combine dodging with blocking.
Not sure about the magic system yet. I've only grazed this so far. I like that one has to learn the system... magic should offer some mystery, right? But I read all this stuff about 'fat mages', etc. and wonder if the magic system offers any real sense of depth in its mechanics at all. I grow concerned that I'd start to explore this, discover it isn't as well-conceived as the melee fighting or the ranged fighting, and get annoyed by the waste of time. To me, depth in magic suggests exploring alternative ways to take down an opponent that can offer surprise. For example, in a dungeon setting with a group of co-operating players, the mage might cast a spell on enemies that slow movement, allowing the others to take them down more easily. Or maybe the mage offers illumination that works only for the party members but not for others outside the party, thus providing an advantage. The mage could have some direct damage abilities, but even these could work in subtle ways that could build on top of each other... first, apply something that causes an opponent to itch, then apply another spell that helps the seeds of that itch grow to some kind of fungus infection that leads to pain. Then another spell could light the fungus infection on fire, burning the opponents with serious, nasty damage. But... no... I don't get the sense it's as subtle as this, for a combat situation. Instead, I get the sense that one learns spells, channels the spell with the hopes of the RPG preventing an interruption or a fumbling of the spell (with some modifiers that reduce or increase the likelihood of this happening), followed by the execution of the spell on the target. Eh, maybe I'd appreciate it more as I get into it, I dunno... I really hope so.
I haven't played around with pets, but it looks promising to me, as I read the in-game material on it.
Yeah, this game has a rough learning curve, but I don't mind that. I do have concerns that one can't effectively learn this game via trial and error that easily... I personally don't like having to go outside of the game to read about how the game works. I would prefer to figure it out from within the game, either via trial and error, or by in-game cues.