I have the Nautical and like it a lot.
- it reads well. It is worth it for collecting (great art ) but not only : it does read easily and well too, in RWS style but with liberty taken in some cards from the traditional RWS symbols and imagery. For me, just the right amount of liberty; with a RWS inspired deck, I love a new take from the traditional imagery, but I also like to see some traditional meaning in the cards.
- it is cohesive for a collaborating deck. It has the best of the collaborative element (many very different styles of art) but also, due to the unity of theme, and due to the effort in presentation, it makes for a cohesive whole.
- cardstock is ok, not the best IMO but ok (but I am very difficult to please when it comes to cardstock). Here cardstock is good enough, not flimsy in the least, but not super luxurious either. I suspect it is a little fragile and might crease easily if bended, so I am very careful with my deck. Cards are larger than standard decks, and personaly I have to shuffle from the short side instead of the large side (overhand shuffle, if that makes sense)
- seller is EXTREMELY nice and helpful and a pleasure to deal with. When I ordered my deck from Etsy, a glitch occured, and she was really the best person to deal with. Customer service says a lot, and hers is just great, 5 stars.
All in all, I would say that, it the deck appeals to you, it is a good investment.
I do not have the Carnival deck, and can only speak of the Nautical. I hope it helps.