I just finished watching the series – and it is without a doubt one of the best anime I've had the distinct pleasure of viewing. The pacing is tight (though perhaps slow in the middle), the plot and characters are endearing and complex; the animation is often breathtaking in detail and fluidity.
The soundtrack, by Fullmetal Alchemist composer Michiru Oshima, is rich and evocative. The ending theme “OVER NIGHT”, by Aya, fits extraordinarily well. I could go on and on for ages about the powerful use of symbolism or the sheer awesomeness of spellcasting poets – but then I'd be taking up time better spent experiencing it for yourself.
If you love anime or even if you just enjoy works of media that reach the level of art, then you owe it to yourself to watch “Le Chevalier D'Eon.”