My thoughts:
• Don't give me decks. Just throw at me some random cards and I will find a way to play them (I see you come up with same idea). This will remove problem where I play only SEEK cards, for example.
• Give me a reason to kill monsters. And not just "lvl up your hero" - because I still don't know why should I lvl up him in a first place. To kill hard monsters? No, I'll put them behind hero and done.
• Add some layer of strategy in the game. Like, reason to put monsters in this room, and not in that. Reason to guard treasures with monsters. Reason to make heroes life harder
And here how I would fix this:
• Give me +1 card each turn, to the max of 10, and then withdraw random card if I reach limit.
• Add "End turn" button, so I could skip some turns, if hero is still running in right direction, or I don't have cards to play, or I don't what to play them now.
• Don't limit player on how much cards he can play.
• Make cards to cost Manna crystals (for example). This will add layer of strategy, where I will choose between playing few cards at once or one high cost card.
• Link heroes lvl with Mana crystals. Now I must kill monsters to get lvl and get even more mana per turn. (for example, max. manna per turn = heroes lvl.)
• Add some "combo bonus" to the cards. For example, if I put item and a monster is the same room - I get bonus for doing this. This will force me to combine cards together: put item in the chest and give key to monster, put water monster in water room, put torch in a room and add flower monster...
• But make "combo bonus" useful. Like, give additional gold, if items are hard to get and monsters are correctly placed. And for a gold you can buy... rooms!
So, gameplay will look like this:
I have 5 cards at the beginning, few rooms and a 1 lvl hero, which gives me 1 manna.
Turn 1 : I start by placing free card: "rat". Hero kills it and gets lvl, but I get 2 mana per turn now.
Turn 2 : I have chest and a sword, but each cost 2 mana. I put chest in farthest room, so hero could not get it next turn. So, at heroes turn he moves toward chest.
Turn 3 : At my turn I will put inside chest this "sword" for 2 manna. Now this room with "chest" and "sword" has "combo bonus". On the heroes turn he will get inside, get his sword, but I'll get +50 gold.
Turn 4 : Now I can go and buy new room... and when I do - I get room with a pot. I can put item inside, or monster. Or both, making this room with "combo bonus". But I don't have "monsters that goes inside pot", so I will play something different, in hope to get this monster in next turn...