Note: I'm going to give the same review to all three "Omnibus" editions in this series, as it is ultimately a single story in my opinion. I can't imagine reading one and not all nine books in the series.
This series is very much worth taking the time to read. It has a full set of heroes, epic battles, soul-searching characters, love stories, revenge, despair and hope. Ultimately, it's a story about family -- in loose terms -- interconnected lives over millennia.
The theme of fate ("urd") vs. free will is obviously a huge theme in the series - it's what drives the story, in fact. The discussions of whether or not fate is predetermined by oracular visions late in the series gives you a lot to think about.
There are portions of this that are very dark (horror in the Lovecraft style, almost), it is very adult - not for tweens for sure. There's blood and gore and sex. But it's still a wonderful story (I guess made even more so if you are into blood and gore and sex).
I said in a review of another of the author's works: if you're a scholar of NW European mythology (Skaldic/Germanic/English), you'll either love this or the required variance from the original will distract you. Remember that this is a work of fiction, not a retelling of the Völsunga saga, Eddas or the Ring Cycle - don't go through and try to compare to the source material!! :-)
It's very well edited overall. One thing I noticed - this series was earlier in the author's publishing career, and you can tell that proofreading got better as the series progressed (misused/misspelled words and grammar errors are one of my pet peeves, but even Tolkien had to correct those in the various editions of his own works). Later works have less errors, in fact.
Overall, I would definitely recommend this book - read the samples, decide if the writing style is for you, and if so, read them cover to cover!