The Lions of Al-Rassan by G.G. Kay is a complicated tale. It doesn't have the sweeping scope of the popular Game of Thrones series but the world of Al-Rassan is comfortably familiar, based as it is on the Iberian peninsula of our own world (well, at least somewhat). The story is as compelling as Martin's series, though, and Mr. Kay's characters are as fully developed as any in the genre.
That doesn't answer your main question, though. Should you buy this book?
Tough question, and probably a bit hard to answer.
Do you like compelling characters? This book has them. Not all the characters were three-dimensional, but the ones who should be were. By the end of the story I actually had tears in my eyes; that might have been allergies, but I don't think so.
Do you like heroes? Villains? Heretics? Zealots? Oh, yeah. You can find them here and you won't be disappointed in them.
How about intrigue? This book has subtle plots within plots, and explained to the reader just as subtly (which made me happy, so I didn't feel too stupid that I didn't get some of them).
Action? Well, of course! War? Sweeping panoramas of it, yet never is it trivialized. Swordfights? Oh, yes, and I have to say I think the author writes action scenes well - they certainly captured my attention, and I could see the swordplay in my mind's eye as I read. (That doesn't always happen for me with some writing styles.)
Romance? Yes, in a myriad of interplays that made me ponder how it would all work out.
I'd go into details, but there's too much. Let me sum up.
This book captivated me and held me through the end, kept me wondering what would happen next (and that isn't usual for me, either), and eventually wrapped it all up in a package that was - well, I won't spoil it, but I was a bit melancholy when I finished.
Buy it? Absolutely. Right now.