Well, someone has to start this off. First let me say I really enjoyed this game and plan to play it again after I spend a few days catching up on everything I put aside to play it for a month, so my criticism is meant to be constructive. I found the story to be both complex and ingenious. It certainly helps to have played Nehrim first to understand where this tale has its roots. It is also rather ... Germanic ... dark & philosophical; I could almost hear Wagner in the background. I really applaud the translators, I think they did an excellent job with what must have been some challenging concepts to translate fluidly from German to English.
For RPG players who are looking for a meaty story, this certainly provides that. For a free mod, you can get away with that. But I think if it were a commercial enterprise where the casual gamer client is needed for financial success, it might be a more difficult road, for a couple of reasons. First, some of the books are quite lengthy, and it takes a lot of patience to read all the way through all of them. Second, some of the scripted dialogs are very long, and some players could be tempted to just click through them to get to the end of the dialog and get on with playing the game, perhaps missing something important in the process.
It must be remembered that this is an RPG; for some, the "R" - role - is important and they really want to get into it, so the story is vital for that. However, for some the "P" - playing - is more important, and they want to focus on exploring, combat, magic, loot, etc., and for them a more slender story would suffice.
The bottom line is - who is the target audience? For a free mod, less important than for a commercial enterprise.
There is also a question of balance, and I don't mean in terms of combat, magic, armor, weapons, etc., but of the overall design of the game. Quite clearly, sureAI put much effort towards designing a beautiful and interesting world setting, and they also put much effort into the complex story. But I feel the effort on story overbalanced the "playing." I understand the problems, that they had one arm tied behind their backs because they had to work with what Bethesda gave them to start with (so I can't criticize the crashes and all the Ark loading screens), and that as some of their team departed, they just couldn't go down to the local employment office to find a quick replacement for such talent. So I lament that the" playing" (meaning the unfinished quests) didn't seem to receive quite the same emphasis as the story and setting did. I'm sure they wanted it to, and I suspect if they have the time to finish the remaining multiple quest lines, those will serve to enrich the story even further, as well as the "playing."
I also just want to complement the music and voice acting, both of which were very superb.
[sorry for the lecture, but I'm a retired professor, it's what I do!]