I got the hard badge on my second game. It's a fun game, but not so much hard as luck. A couple shield 5,000 point upgrades and 80,000 points comes in only a few minutes.
Once you get use to the controls and the physics of your gun, the game is pretty interesting. The screen shake is a bit too much, however, and should be drastically reduced if not eliminated.
I agree with Orona. Great game, but the black samurai are too good. I know they are expensive, but at the point you can take the town, you have an extra 50,000 gold to buy a full team. After I loaded up with black samurai and had Patriotism maxed, I lost only one for the remainder of the game.
First level is obvious. After the first, buy one soda can. After the second, buy as many soda cans as possible. After you max soda cans, buy skis. After you max skis, buy Freaky. After you max all 3, buy gunpowder, then buy the modifications. You should be able to buy all the upgrades at the 5th level and beyond (sooner if you do well). Aim for 45 degrees, and use all your soda cans right away. Then use your skis, followed by Freaky. Easy to get 7,000.
The star slide works just like sliding on the surface of the water. Just make sure you are vertical and pressing on the down arrow when you are passing up or down through it.