I always like decks that find interesting ways to represent tarot symbols within whatever theme the artist has chosen. Sometimes it's doesn't work out so well, but this one, I think, makes it happen. The wands are oars, the swords are tridents, the pentacles are either bubbles or glass orbs (but either way, cool), and the cups are seashells. I also love the color schemes...especially, the swords; there's a nice dark vibe without being murky.
I can't speak to the physical attributes, because I don't actually own this deck, but of what I've seen, the only negative I can find has to do with the Pentacles, and it's minor. Most of the cards stick closely to Waite-Smith visual cues, but the pentacles get a little iffy here. The general idea is there, but most of them are just pictures of mermaids either gathering up or just being near the bubbles (or glass orbs). But you do get the sense in most of the images that the orbs are valuable in some way, so it still goes along the lines of what pentacles represent.
It also doesn't hurt that the images are plain old beautiful. And it looks like the artist paid attention to making sure the mermaids were all shaped differently, which really creates a world, avoiding a cookie-cutter Barbie doll effect.