Robin Hobb seems to alternate her trilogies: one will be amazing, then one will be ok, then one will be amazing, then one will be ok, &c. The Soldier Son Trilogy is definitely the latter - just ok. Not mind blowing, but also not mind numbing. Walking the line between subject matter that piques your interest a little, versus subject matter that really grabs you and engages you.
High level plot summary: Nevare Burvelle is the second son of a New Noble - which is to say nobles elevated to their status as a prize of war, rather than by inheritance. As a second son, it's Nevare's place in life to enlist in the military, train to become a cavalla officer, and make his family proud defending the country. Unfortunately, Nevare gets caught up in the magic of his country's sworn enemies, and the two forces war for possession of him. Book 1, Shaman's Crossing, primarily follows Nevare's entry into the military. Forest Mage recounts his status as an outcast and struggle to stay in his world when the magic is pulling him away. The final book, Renegade's Magic, largely focuses on Nevare's role in the magical world. There's obviously a lot more to it than that, but I'm already edging close to spoilers, so that will have to do.
I think I proved in my review of Territory that a story that's good enough can make me get over any preconceptions I have about how much I'll dislike the world. When I started Shaman's Crossing, I immediately recoiled from the very harsh military aspects of the book, and considered putting it down for a while. Luckily, Hobb developed Nevare, his supporting cast, and the magical world surrounding them well enough that I stuck with it. Honestly the book had some Ender's Game-ish overtones... but I suppose that's to be expected when writing about the hazing that teenage boys are capable of.
Forest Mage really did the best job of the three books at showing off the Angst that is Robin Hobb's specialty. Let's face it - she does angst better than anyone else out there. She just has a way of making it really hit home and be believable. So while I never got all that into the second book... never really saw where it was going, or what the expected start and end points were - boy did she ever twist the knife slowly. The Whole Damn Time. Ouch.
I really thought that the final book would be my favorite of the trilogy, as it had the most fantastical focus, but it just didn't grab me all that thoroughly. I think it's largely due to the fact that I never liked the supporting cast of the last book as much as the cast from the first two books, so basically the only person who got screen time that I gave a damn about was Nevare. I didn't really care about the feelings or fate of anyone else in the 3rd book, and that did a lot to detract from the plot.
Overall though, I feel like the characters weren't as well developed as I can usually count on from Robin Hobb. Her emotional wrenching is largely based in the fact that she creates such vivid, engaging characters, and that was really lacking here. It's too bad, because the world she crafted is quite interesting and original - I can't think of any book I've read that has anything like it. It just seemed like the big overarching themes never quite connected with the actual people and situations. It's hard to put my finger on.
Hmm, this review is sounding more mediocre than I intended. I've mostly been comparing Robin Hobb to herself, which isn't entirely fair, because she's still leaps and bounds above the majority of other authors I read. This trilogy is no exception - it really is a good read, and worth finishing... it's just not quite as shiny as her Farseer books, for instance. I also think that people not quite as off-put by the military theme might enjoy it even more than I did; it can be hard to really get back into things after a start that rocky, regardless of how great the story is.
Hmm. I'm rambling a lot. Bottom line: it's good, read it. Be ready for Hobb's Trademark Angst - you won't be disappointed (though you may wonder if she's starting to go a little soft in her old age).