It gets really annoying when the balls are pretty fast and you pick up a powerup and everything freezes. It throws me off, at least. Have an option to shut that off, if possible.
I don't see why people complain about the challange. Simply make the computer a custom deck with no monsters, and then lots of monster buffs and heals. They won't be able to use anything and you'll win automatically.
The games font is impossibly small to read on my screen. I just had to guess if I had the money to buy things. So, until I can actually read the game to enjoy it, I'm giving it a 2.
Big fan of tower defense games here, and I like this one. A few suggestions to make the game better, though.
Add some kind of restart button. Its annoying to have to either lose entirely or refresh the page to restart.
I've had a problem with the 'impact tower'. It will target an enemy and 'charge' for a few seconds, and if the enemy is killed before it fires, it will just sit there uselessly for a few seconds as if it fired instead of targeting a new enemy. A few of the towers do that.
Also, if enemies are traveling in a path and you put a tower in their way, I've had multiple instances where the enemy will just sit there without moving until I kill it.
Great game, but a few bugs stop it from being really good. 4/5 for now.
Unless the disease starts in Madagascar, its pretty much impossible to win. You should add an airport to Madagascar, or at least make it so the odds of ships going there are a little higher.