I beat Los Muertos and Volk in two hours- It took me another hour for Shai-Gen (The last few are really, teally hard), and got 4-star in everything in about 45 mins. A star is your skill level in that skill-eg. 4-star shooting skill means you are really accurate, 4-star strength means you can lift asbout 4 tons and throw it... um... far. It's really easy to level up. Just concentrate on each skill at a time- good luck! :)