It's really hard for me to somehow rate this book. You see, on the one hand, it was really good - the story was quite intriguing and well plotted - on the other hand, quite often I asked myself if the author had even seen SGA. Why? Well...
a) He got some of the most basic SG "hard facts" wrong - according to him, the 'gate wormhole goes both ways!
b) The characterization. Oh, boy. Teyla kept snapping/barking/snarling. Rodney either whined or he was painfully meek, his acerbic - and intelligent - humor was completely absent etc. etc.
c) The author moved the plot forward through completely illogical decisions on the part of the main characters. Example? Carter forced Sheppard to take Keller, an untrained doctor who refused to even accept a gun, with his team - on a recon mission to a possibly hostile planet! When Teyla and Ronon were kidnapped in a space ship, Sheppard and the Marines went searching for them - on foot!
d) The author's style... If I hear "the Athosian woman" or "the warrior woman" or "the P-90 submachine gun" or "the submachine gun" again, I will scream!
I think that Swallow would benefit from either having a co-author or a better editor.
To sum it up? My least favorite SGA book so far. I won't be re-reading it any time soon, that's for sure...