In a small game like this, toggleable stuff could make it more interesting. The ability to toggle autofire, platform size, monster amounts etc would provide a whole new challenge. I'd like to see more levels and weapons aswell, I love the game as it is already but it could improve a lot.
To the Extreme!
Dude! You just completed the To the Extreme! achievement in Onslaught2 and won the To the Extreme! badge and 30 points! game over at exactly 1500 kills, pfew :P
Dude! You just completed the New Challenger achievement in Mytheria and won the New Challenger badge and 5 points!
Dude! You just completed the Black Lotus achievement in Mytheria and won the Black Lotus badge and 15 points!
Dude! You just completed the Complete Card Conquest achievement in Mytheria and won the Complete Card Conquest badge and 15 points!