Sorry that I missed this earlier - I hope you don't mind me starting the discussion a bit late.
I thought it started out quite well - sure, traditional epic fantasy with nothing particularly new about it, but it was still entertaining. There were some interesting ideas that I feel could have been much better used by a competent author - including the style of having it as if it's a translation of an evil text (though sadly it felt more like a rip off of ideas by CAS and Lovecraft). But the books declined very rapidly after the first one. I enjoyed the first one most of all partly because it was the darkest, it was the most original, best written and most realistic of them (of course, not at all realistic compared to authors like Martin).
The second book was badly paced, full of description that tended to work, annoying events including dead characters coming back to life and a more stark delineation of good and evil. He seemed to look for what cliches had been forgotten in Wit'ch Fire and added them to Wit'ch Storm. The central idea of the magic had some pretty awful aspects to it - eg combining the hands to produce storm fire, having them renewed by moonlight/sunlight - being ill defined and basically it was just a deus ex machina in preparation.
But it was readable - barely.
Wit'ch War was one of the worst novels I've ever had the displeasure of reading. All the problems remained from the earlier novels, but it seemed to combine pretty much every problem any fantasy novel has ever had. Cliched, badly written, incredibly unrealistic characters, slow moving, predictable plot, an unrealistic magic system ... the list goes on.
A few things that really irritated me:
The use of apostrophes. How idiotic was it to put apostrophes in the name of pretty much every race and most names. I can excuse Erikson - he has a few names, 3 or 4, out of a cast of hundreds or even thousands. Clemens has closer to 20 out of a cast of 30.
Good v Evil - ok, so it's possible to write a good book with this in. But the evil here just seems ridiculous, but worse, it's not that it is pure evil, but that the actual idea he showed in the beginning of the first book was so much more promising. If Clemens had the talent of Martin, I could see this being an excellent series - the potential is there, yet Clemens does his best to make you hate the series by taking good ideas (an invasion of a continent, the defenders lose, a resistance movement) and ruining them (but actually, the defenders were good, the invaders evil beings motivated only by evil and the resisters just go and have to find an omnipotent book, and wow, what a coincidence, a wit'ch was suddenly discovered that can go and get the book for them - and realism - what's that?).
Characters - far from Clemens' strong point. There's no consistency to them, let alone realism. The obvious things out of the way first, they're all good/evil archetypes, the good have no flaws to their names and you can fit almost every one somewhere into a D&D manual. Problems - again, missed opportunities (Tol'chuk - what an idiotic quest, why wasn't he killed? Compare how Erikson treats Rhulad Sengar and the Tiste Edur culture to how Clemens manages to make the og're culture a simple archetype and Tol'chuk treated indifferently).
But one thing that stands out for me is Er'ril, who is possibly the single worst written main character in fantasy. I've said he's an archetype, but that's only part of it. He's inconsistent and couldn't be much more realistic. He's supposedly lived for 500 years. And has he changed at all from a young man? Have the supposed terrible experiences of that time affected him an any way? And while he goes around slaughtering goblins and evil minions without hesitation (and happens to be one handed - and then he gets another hand- so obviously cashing in on Martin without the skill), as soon as one of the women (forgotten who it is now) says she gave those with the ability for magic poison for their own good, he's shocked and can't believe she'd do such a thing (and neither could Elena or the rest of the cast), and it's supposed to be a flaw in her character, which it quite clearly isn't. And then in Wit'ch War, Er'ril effectively dies and comes back to life - or at least, there's a scene where you're meant to assume he dies, and then you find out that actually he's fine, and he's just been captured, and he gets rescued a bit later.
And then there's a huge, pointless sequence with Elena running around rescuing him, not getting caught because, we find out, she can turn invisible as well as everything else, and then the ending is one of the most predictable endings in fantasy.
To conclude, Clemens is a talentless writer with occasional flashes of imagination IMO, who wastes every opportunity he gives himself, puts a lot of filler in his novels, but could, perhaps once have approached being a decent writer, maybe on the level of Feist if he had tried to write a decent novel (and the whole of the Banned and Banished series could easily fit into one 800 page novel if the filler's taken out) rather than a populist commercial novel that has really nothing to add.