I'm too old and there's too much dust on the AD&D books in my closet for me to really love this book.
This was Elizabeth Moon's first published novel, and the first book of hers that I've read. It was a free download from the Baen Free Library (which I highly recommend for anyone looking for cheap reads; Baen has made available novels from dozens of big-name F&SF authors). Frankly, it was a struggle to get through it, and if I weren't the sort who hates to leave a book unfinished unless it's really bad (which this wasn't), I probably would have put it down after a couple hundred pages.
So, here's the story: Paksenarrion Dorthansdotter ("Paks") runs away from home to avoid being forced by her father to marry a pigfarmer. She joins a mercenary company as a 0th-level Fighter, goes on several campaigns, and acquires enough XPs to level up to where she can start her career as a 1st-level Paladin, which I understand she does in book two of the trilogy.
Now, in fairness, the writing is not bad, so this doesn't read like a straight novelization of a Player Character's saga. If I hadn't been such an AD&D nerd back in the day, I might even have been able to read this as straight fantasy without seeing character sheets in the background. However, the setting really is straight out of 2nd edition AD&D. Elves, half-elves, dwarves, gnomes, orcs, fighters, paladins, mages, clerics, thieves, assassins... just about every character is readily identifiable by character class and alignment.
That said, it's not bad for the sort of book it is. Moon is a decent writer (at least in this, her debut novel; I know she's very popular so I assume she got better). Paks is a believable character who goes from naive recruit to skilled veteran without becoming a Mary Sue, and Moon avoids rubbing the gameyness of the setting in your face too hard; you don't get the awkward sense that once Paks picks up a few levels, she can shrug off wounds that would have killed her earlier in her career. But I didn't find Paksennarion all that interesting as a character. She's brave, naive at first, a little idealistic and ambitious, and (as mentioned several times in the text) completely uninterested in sex, which means no romance of any kind. That's fine with me, but there's not much else that seems to motivate her, other than "Become really good at being a fighter." Only at the end of the book does she begin to show signs of thinking about the world a little more deeply, and only a little.
The story follows Paks through her first three campaigns as a mercenary. First they go up against some other merc companies and militias in a routine feud between city-states over tariffs and such. Then they engage in a more prolonged campaign against an evil overlord. Along the way, Paks has some minor solo adventures. Standard low-level AD&D character progression.
The AD&Dishness was also evident in the way that nobody blinks at women fighting alongside men, or becoming knights and paladins. I do not object to the concept of an egalitarian society where women warriors are accepted, but when the world otherwise seems to conform completely to your basic pseudo-medieval pseudo-European setting, complete with traditional gender roles for all the women who don't run off to join mercenary companies, it seemed awfully convenient that a woman can join the adventuring classes as easily as she can in an RPG.
I'm kind of curious to see how Paks's character development proceeds from here, and how Moon handles paladins (is Paks going to get healing hands, immunity to disease, Protection from Evil 10' Radius, the whole package?), but considering what a slog it was to get through book one, I am not eager to continue her story right away.
On the plus side, Moon does a great job with description. The medieval towns and villages, their layouts and architecture and furnishings, the food, life in a merc company (including the training, the drilling, the latrine-digging), and the military encounters, all get a good amount of detail. The magic stays mostly in the background -- we see a spell here and there, a couple of potions and minor magic items, but nothing epic enough to alter society (or turn the fighters into an undifferentiated mob of fireball fodder, like they are when a high-level mage shows up in an AD&D game). The non-humans are only briefly mentioned, as the story takes place entirely in human lands.
Summary: Worth reading if you like generic epic fantasy, a better AD&D novel than books that are explicitly labeled as such, but not really exciting or original. If you're still in the "writes AD&D fan fiction" stage, and especially if fighters are your favorite character class, you'll probably love it. And like I said above, it's available for free, so worth a download if you're in the mood for some light hack'n'slash fantasy.