Vision of Escaflowne is unique in that it is one of the few anime series that manages to deviate from the typical "good guy kills bad guy, bad guy dies" plot and yet does not degenerate into rambling poetic chaos. Its plot roughly follows a "good guy fights bad guy, bad guy turns to good guy" storyline. Oh, that's in addition to the beautiful animation and backdrops too.
The mecha design is excellent work - outlandish enough to constantly remind you that this is most definitely not Earth, yet sylish enough to make you hungry for another mecha fighting scene. In-between the fights, the sub-plots keep you glued to your seat. You don't find yourself asking "so, what happened next?", simply because they flow so well. You hardly have enough time to digest what you've just seen before scene smoothly transitions into the next sub-plot, or another fight scene.
The story is driven by lots of philosophy. Hitomi dabbles in tarot readings while Donkirk drivels on about Destiny. Alan and Van never stop wondering what their purpose in life is. Nothing as deep as Serial Experiments Lain, but it's enough to get you thinking about the characters, so you don't sit through the entire series with a blank look on your face. the poetry isn't in the storyline; it's in the dream sequences. Enjoy them while they last
The characters are human. Not in the I'm-too-weak-too-help-myself way reminiscent of the children of Neon Genesis Evangelion, but in the I'm not just some cute guy/girl-with-personality-quirks way. Alan is a big flirt, and he hates his father. Hitomi is inherently selfish and hesitant. Van is inexperienced and arrogant. The way these faults play themselves out lend lots of credibility to the characters (their actions never feel unnatural to me), and to the overall experience that is Escaflowne.
The bad guys are not for comic relief, and neither are they there for the hating. Folken, the anti-hero, is hardly hateable. He has his own side of his story, and *surprise* it's not one of those I was once good but something happened and now I'm full of hatred stories. He was misguided, and after he realises his mistake he is truly regretful. In some ways I liked him more than I liked Van, and I really felt it when he died near the end of the series. Dilandau may seem like another psychotic maniac, but there's good reason for that. His character is not as thoroughly explored as the other main characters, but he has the distinction of being the most surprising twist in the series. Donkirk is hard to like, but you will admit that he has good reason to do what he does. He's a scientist at heart, and a rather cruel one at that. Even he, the most mysterious character in the series, has his story, and short backstory that is explained in the series. This fact alone is testament to the depth of character development evident thrughout the series.
The only part of this series that lets it down is the ending. Everyone I know who has watched the series asks the same question right at the end: That's it? This series deserves a more cathartic ending (but sadly does not get it, even in the subsequent OVA, A Girl In Gaea). However, it does not detract from the whole Escaflowne experience - it's just a minor detail that could have been done much better.
As mentioned in bishopred1's w/u, the storyline suffers from minor inconstitencies. Again, these do not kill the series, but they are irritating. Try not to notice them. And no matter what your circumstance, never settle for the English version. The horrible voice acting will completely put you off and give you a really bad impression of the series, even before the real thing has a chance to impress. Do yourself a favour and get the Japanese version. Most of them will have English subtitles (which are somewhat poorly translated, but they'll do). Enjoy.