Great series. Though I don't really like its graphics (I usually do watch more "realistic" looking animes, if this makes any sense), I just couldn't stop watching it all the way until it was over.
I heard about this anime in the naruto thread of TL, and after I watched the first episode, I had mixed feelings about it. It seemed that it had every bullshit what you can find in any anime/manga (magic, mechs fighting, failed stupid references to European culture, masterminds playing each other.. etc.), but the story was exciting from the start.
The real rollercoaster started from the second episode. Basically after that, you just shit your pants in the end of all the parts (including the last one! ). The turning points are often better than the ones in Death Note.
It is "only" 50 episodes, each 20 minutes long, so not too extensive. Definitely it was worth watching, even if you hate mech fighting as I do.