I like the idea of them, and the original shards worked quite well IMO.
But I feel like the recent ones haven't been quite handled well in terms of theme... and the result is that there are cards coming out that have simply been made other and given the name "Shard" rather than shards themselves.
Shards to me are exactly that... They need to feel like they were once a "Part" of something, much like relics, and to me they need to display a virtue.
Shard of Divinity and Shard of Gratitude embodied this perfectly to me, and Shard of Readiness was still okay.
I could just as imagine "Divinity" and "Gratitude" from them, and I feel that's important. They feel as if they are part of a great power, which you can draw upon only a small amount.
They have a certain level of "Permanence" that fits thematically with shards to me, and they are also utility cards- Useful in many situations.
These are the what shards mean to me, and through this concept, I like the idea a lot.
But out of the three, Readiness feels the most misplaced to me. While it does embody Readiness as a virtue, it doesn't quite make sense to me as a shard concept.
What is it a shard of, really? I can't quite imagine the raw force of "Readiness" as much as "Divinity" (Looking at the FGs) or "Gratitude" (Life gain in general).
As for the new shards, Serendipity is the best approached to me, except the name is a little bit awkward. In general though, I can definitely imagine the "Serendipity" it is coming from. It is a small part of the raw potential of all the cards out there, in all their possibilities. While it really only works well in rainbows, it works with enough utility that I like it nonetheless.
Void is the next one that still feels okay. I can imagine the Void itself which it draws its name from. It makes sense in general, and works well thematically. It's just that the theme feels slightly off compared to the other cards, which embody virtues. However, if we extend our understanding of shards past just virtues and any general underlying powerful force in Elements, Shard of Void works well as a shard. It is IMO just slightly underpowered, but that's not a problem with theme.
The other shards though...
Shard of Sacrifice is just too powerful to be a shard IMO. It doesn't feel like a "Shard" of sacrifice, it mind as well be "Sacrifice" itself. It's too off to me...
The mechanic is fairly complicated and doesn't have the same underlying simplicity of the other shards. Instead of a raw power/energy/force it feels very specific.
I may be wrong, but it really feels to me like Zanz planned the Shard Revolution AND came up with a "Turn Undead" concept at the same time and decided to just make it a shard. The result is a slightly out of place mechanic amongst the other shards. IMO, it would be best to completely redo SoS and make the undead mechnic a different card, but that probably won't happen.
Shard of Patience on the other hand, suffers the opposite. It's clearly underpowered. But the only reason it's underpowered is the mechanics of the game. In the end, there are only two types of decks really, decks that are designed to make yourself faster than your opponent, and decks that are designed to make your opponent slower than you. Everything will fall somewhere between that spectrum. But what Shard of Patience is really trying to do is make yourself slower to make yourself faster later... And the make yourself slower prevails. The shard concept is not bad, but as it is it's too situational to do work well as it is.
For the In Development shards:
Shard of Conscience feels works well in general, but I only worry about it being situational. But at the moment I can't think of much better and haven't tested it, so oh well.
Shard of Focus feels like it's just another card given "Shard" as the name. It would work better as a gravity card, not a Shard. What is this "Focus" that it's a shard of? The raw destruction of permanents to grow larger and burst into a black hole? No, it's to specific to be a shard and needs fixing IMO.