Something I really, really appreciate about the design of the game is how the deckbuilding aspect works. In a traditional CCG like Magic/Hearthstone/whatever, you have this fundamental feel-bad problem where you need different cards in different stages of the game. So you’ll have a bunch of early-game cards, then some midgame cards, then some lategame cards, and you have a few cards that are useful all around.
But, well, for the sake of example, I’ll talk a little bit about my experiences with Anyfin Paladin in Hearthstone: I’d have tons of games where I’d be in a tough situation, and I’d have the ideal card to deal with that situation…except that the card was still in my deck, and I hadn’t gotten lucky enough to draw it. That feels really bad. And instead of having those cards, I’d maybe draw cards that aren’t useful in the early game. So I’d spend the first few turns getting blown out of the water by an aggressive deck for the mere reason that I had only drawn early-game cards, or I hadn’t lucked into any of my card draw.
I think it’s telling that in traditional CCGs, cantrip cards and card draw are valued immensely, because they increase the chance that you’ll get lucky and draw into the cards you need, out of the entire deck you have. Also, every traditional CCG has a mulligan rule, because of the possibility of getting a terrible starting hand of cards you can’t use in the early game (or not getting enough early-game cards)–and there’s no mulligan in Codex, because it’s not needed.
But in Codex? If you don’t need a card until Turns 5-7, then don’t tech it in at first. Your Tech 0 cards are exactly what you need to handle the early game, and you can tech in midgame and lategame cards as the turns pass. It’s a really brilliant bit of design that makes a huge amount of difference. Suddenly, instead of crossing your fingers and hoping that you draw the right cards for your situation (or, in the case of Hearthstone, a card you can play on the mana curve), you mostly get decent plays for your situation, presuming you’ve teched well. To top it off, you get to start workering cards from the get-go, slowly filtering the weaker cards out of your deck.
It’s a great cycle that, I think, promotes decision-making and skilled use of your resources. Plus, the game doesn’t totally remove randomness, because randomness does often lead to more-skilled play. You have to figure out what the best response is, given a limited set of options. I think that Codex hits a Goldilocks level of randomness here: it dispenses with the feel-bad “I hope I draw Card X” of traditional CCGs but keeps a “well I don’t have exactly the card I need, but I can use these cards” level of random draw. I really like that.