I know lots of people have already said this, but I'm going to say it again anyway: Please make it so that we can see where we can build. I waste a lot of precious seconds trying to find a place to put another tower while I'm being attacked by aliens. If I already knew where to put my building, things would go a lot faster.
I found a pretty bad glitch. If you suddenly switch to a bird when Theo reaches the level exit, you won't be able to exit the level, and you can't use any commands. The only thing you can do is quit the game. I accidently did this at the end of the 3rd level and when I selected "continue" at the main menu, it sent me back to that fight with Vandheer Lorde.
Ugh. I was just about to beat the boss when a combination of pressing space and clicking made my screen scroll down and he got on top of me and killed me.
What can I say that others haven't said? Gold is the most used resource, the other two are underused, making gold overpowered. The browser and deck should be combined into one. I should be able to tear up new cards without having to go to my deck remove some cards, add some new cards, go back to browser, delete the new cards, go to my deck, and add back the old cards. It's way too tedious.
I don't know if it's like this for the rest of you, but this game is really laggy. I've never really had any lag problems before with any of undefined's games, and my computer really isn't that old or bad.
The problem with harder difficulty and above is that everything is now based on luck, and you have a higher chance of bad things happening to you than good things. If you are lucky enough to start in a good area and acquire a few good buildings, you will get one unlucky random event after the other. And if by chance you somehow gain happiness, events will conspire such that those random events will take double the happiness away from you. It's a good game and all, but harder difficulty just seems to suck all the fun out of the game.
Another thing I'd like to add is that the rage attack (F) is just too weak. When you use it, you stand still for a moment and then cause an explosion to happen over a small range. It's way too easy to get hit while that happens, and the attack range is nothing special. Dropping bombs is more useful than this attack. I'd suggest either giving the rage attack a much bigger range, or having it have some other effect like "invincibility for 5 seconds", or something like that.