So I purchased and beat this, and I have to say it was worth every penny. It's got a couple of very minor bugs, like a one piece of dialogue that didn't have an associated sound and one piece of dialogue that had an extra word and bit of silence at the end of it that obviously wasn't supposed to be included. Also, the music in the training area of the priory is dungeony music... which doesn't seem entirely out of character when you first explore it, but it never changes even when it gets fixed and inhabited. Lastly, the priory shrine in the chapel doesn't seem to work and always tells me to repent my wicked deeds, despite the fact that I have no bounty on my head. I can't 100% confirm this as a bug, but I'm pretty sure I got blessings from other shrines just fine. Still, that's pretty much a non-issue anyway. For the most part, everything worked great! Quests were all really fun, and a few were surprisingly deep, those making up for a few that were a bit too simple. It's got a nice little story to go with it, some people to get to know, and by the end of it you've been all over the place, seen some unique stuff, and fought some cool bad guys. I really couldn't say how many hours it was, being that I didn't play it straight through (I can't do anything straight through in this game... I'm easily distracted), but I do know that I didn't fully explore the one really big dungeon that's included (there are a couple, but I'm talking about the most significantly sized one). Difficulty was about standard, though there were definitely some tough parts that took me by surprise. Some nasty zombie mobs in one spot that were really hard to kill, and a couple other places where you've got the potential to get gangraped by a large number of mobs at once.
So yeah... anybody that's been holding off, don't bother. It's really great. I'd say go for the retail package and get all the other stuff, too. I really don't care how pissy people have been about all this, but the downloadable content mods thus far have all been really great. For twenty bucks with the retail package you're getting an awful lot of small stuff that just makes the game nicer. It's certainly far from necessary, but I had fun exploring all the new stuff and playing with the new toys. And I'm surprised at how well the game has stayed balanced. I still feel like I'm very much earning all my rewards, and there's still plenty of challenge.
I'd give Knights of the Nine an A-, or thereabouts. High 80s, whatever. Retail package is a little bit slapped together install-wise, but the content is good stuff. Small stuff, but nice.