Having just finished Gaia's Secret (the day before I finished this book, hah), I couldn't wait to get my grubby e-book loving hands on The Keeper's Flame... which I then proceeded to plow through in about 7 hours.
I have some mixed feeling on this installment - mixed because even though I still loved it, of course (like, a lot a lot), I was still a bit disappointed because it didn't hit on all cylinders like Gaia's Secret.
My biggest issue with the book was Daria's complete lack of confidence in herself. Essentially, for reasons unknown (until later on), Daria has lost her magical abilities. Because of this, her confidence takes a major hit, to say the least, and there's tons of self-deprecation to be had. I wish there had been a, "Hey, I don't need magic to be awesome!" realization moment, especially considering that Daria has a lot of physical skills and good instincts - but, nope.
Everything else, though? I'd say it was all great, for the most part. The story switches gears in The Keeper's Flame, so whereas Gaia's Secret was fast-paced and full of adventures, this book slowed things down as it explored Daria's adjustment to her new life. Nonetheless, Daria manages to find herself in more than a few scrapes along the way, and events are constantly in motion.
As a side note, I think that the romance aspect became a bit more pronounced in The Keeper's Flame - it was still not quite front-and-center, but was almost there - so be careful if you don't like that kind of stuff. In this book, too, there were times when the romance teetered on too-angsty or too-mushy, but in the times that it was on point, it was just oh-so-squee.
So, this is the part that now sucks - having to wait for the next (and last, I believe) book in the series! I'm lucky enough with the timing since Breath of Dragons comes out next week (yay!), but even that is going to feel like an excruciating wait right now.