I really like the style of holographic cards in E-Card series. They have just the right balance of "sparkle" to make the cards look appealing to me. The Pokemon artwork itself was often diverse, and ranged from
simple to almost scary levels of
realism. The attacks and Pokemon Powers were often accompanied by chunky paragraphs of text that made the cards look intimidating and interesting. The Crystal cards are just beautiful, and are my favourite kind of "special" rare. Scans don't do them justice, you need to hold one in your hand to truly appreciate their lustre.
My favourite card for looks is
Crystal Crobat. It has a perfect balance of everything. The card art is nice, but not overly detailed. The card background's smooth transitions between faint shades of blues, purples and reds looks lovely without being too distracting. The same can be said for the sparkle: It's there, it's pretty, but it doesn't dominate the card (unlike, say, recent EX Pokemon). The text for the attacks and ability is interesting but doesn't overcrowd the card. And, importantly for collectors, it just
looks valuable. It
oozes rarity. The weird energy requirements and typing are telling you that this is
not a typical card.
And of course, I own it. Crystal Crobat was one of the only holographic cards (not just Crystal, holo in general) that I pulled from those damn E-Card sets. These sets are notoriously difficult to complete. So knowing that I own a Crystal Crobat, one of the harder to find cards in the series, makes it even more valuable and hence special in my eyes. : )