Maybe reading Mark of Nerath caused my expectations to plummet, but I found Seal of Karga Kul to be only mostly forgettable. Considering the usual quality of D&D novels, this isn't as bad as it might seem. The basic plot of the book is that a character is trying to deliver a box to somewhere, gets attacked by stormclaw scorpions en route, and is saved by a group of adventurers that happen to be passing by. The roster is populated by the usual suspects: a dragonborn paladin, human cleric (I think), elf ranger, halfling rogue, and various random strangers that sign up to replace the characters that get killed along the way.
So, main character one joins up reluctantly with the party, something that crops up way too many times throughout the course of the novel. I can't remember how many times he was like, "I want to leave," and dragonborn replies with something like, "Do you want to?/Then leave", and then he doesn't, only to bring it up again later. To mix things up, he would also frequently consider leaving, before telling himself that there's no way he could (only to again consider it later and reach the same conclusion).
As for the other characters, they felt too one-dimensional for me to care about or remember. I recall Biri-Dar's name, but otherwise could only refer to most of the rest by race and class (there was a cleric, but I'm not sure if he/she was a human or what). As with Mark of Nerath, none of the them seem to talk like actual people. Sometimes the dialogue is choppy, and sometimes they talk like they have to use as many words as possible in a single sentence. The author hints at the history for a few of the characters, but doesn't really touch on it enough to make you care, so when the bodies do start piling up, I thank myself that I'm past the halfway marker.
Descriptions suffer from the same faults as the dialgoue: too much or too little, making most of the book very awkward--often times frustrating--to read, as I had a difficult time figuring out who was who, or what was happening. When I think back, I know that they went into a trade town, had to muck around in the sewers for some reason, went into a jungle, met some halflings, and fought some undead. Out of all of that, the only thing that really stands out is when they went into an inverted castle to get a magical quill (or something). That sounded like an awesome dungeon locale with a stock (yet solid) "end boss", and if I could keep a campaign going long enough I'd probably steal that idea.
I wouldn't say this book is bad, certainly not as bad as Mark of Nerath, but as I said it's definitely forgettable. I'd say it scapes the bare minimum as far as quality goes: you could do worse, but you could do a lot better. I'd give it a 4/10.