Just played it once, on normal difficulty, got to around round 20-30.
Nice first experience! Deck building and base defence, a good combination. The ui/graphics is very basic, but the concept itself is great. A nice game loop. Can imagine coming back to it. Is there any active development? I haven't really checked :)
Forgetting to use gold at maximum.
I kept forgetting to use gold to upgrade towers, know there was a hint about it, but I think I was at max gold almost every level where I didn't draw a "Buy card". Kept forgetting, maybe show gold in red when the maximum is reached? To better remind about using it. But I know I'm also forgetful.
More interesting terrain features?
Would be interesting if there was different terrain types being generated. Like water/forest and mountain. Maybe they all block building/enemy movement. But they could also enable special buildings. Like mines generate more money next to mountains. Farm more next to water. Maybe forest can be cleared for extra gold? There are many possibilities.
I did notice one bug:
If I clicked on a card to play, and the menu icon was above a valid tile (A tile close to a road which allows placement), it would place the tile there immediately, without giving me the option to place it myself. It also replaced existing buildings. I accidentaly ended up replaces a sniper tower, felt bad. I assume it happens because the same MouseClickEvent is used twice, once for selected the card from your "hand", and once for selecting a tile to place it on. Not sure how the engine is setup, but if the second MouseClickEvent is blocked this issue would not occur.
Otherwise, a really nice first experience!