I'm very glad you liked it! Which decks did you try, were there any mechanics you particularly liked?
It is just premade decks for now - I've not actually implemented the deckbuilding interface yet and in the meantime the prebuilt decks make it easier to for people to wander in and try it out without having to worry about taking responsibility for the contents of their deck. I intend to open a Steam playtest very soon, hopefully this week, and then getting deckbuilding added will probably be the main thing I want to have in place before I upgrade the playtest to an official demo.
FYI, I've just updated the itch build to include an in-game tutorial/reference guide that I didn't quite manage to get done in time for demo day. If you do try playing it with friends, I recommend using the new build and checking the guide (you can look at it at any time by clicking the "i" button in the top right of the screen), it should hopefully answer most questions you might have about gameplay stuff. And if you do try playing online, please let me know how you get on with creating/joining lobbies! I've tested the networking stuff as well as I can with friends and family and as far as I've been able to confirm it seems like the networking code is pretty solid, but it hasn't really had a chance to prove itself in the wild yet.