I think this is a great game idea! I love deck building and tower defense games, so i was really excited to try this one. It already has a lot going for it in terms of originality especially, in my opinion.
a couple things i would love to see in the future (if, of course, you want to implement them):
-when trying to get a better view of the layout (i like seeing top down for this kind of thing) turning the view shifted what area of the map i was able to see on screen. Perhaps implement a "lock" so that when tilting the map for a better view, it stays centered on the middle of the map?
-it could be very useful to implement pop ups when you hover over certain items, like when your mouse is over the deck a reminder of how many cards are in there, and how much mana it costs to draw. or hovering over an enemy and a pop up says that enemy's name and elemental alignment. a pop up over a tower with a brief description of its power would be nice too.
-DEFINITELY add a more in depth tutorial level, guiding the player step by step through a level. this will help familiarize them with gameplay and cut back on frustration. While the game is relatively simple, this is still helpful especially for players who may be new to this kind of game. maybe make it optional for those that want to jump in?
-visually showing the range of the towers would be very helpful (like a circle of range when you select the tower)
-Honestly, I would also give the corridors a little more space, to show off the character models and the tower effects better.
These are just a few suggestions to make the game more user friendly, which i would suggest prioritizing above new cards or things like that. While the variety would be really fun, if the game feels clumsy to play people may be less inclined to stick with it. I think there's a lot of potential here!