Killzone... Liberation? Because if you mean Killzone Liberation, the police need to be aware you are smoking some premium stuff and confiscate it for your own good. Killzone Liberation is one of the best games available on the PSP and even has a whole new level available to download for free.
In short, Killzone Liberation is awesome and his comment and my whole freakout had absolutely nothing to do with the POINT of this thread, so...
The first Monster Hunter Freedom was cool, it got very hard solo. Honestly never played the second one but I could only imagine that they improved upon it. If you find it for a reasonable price or you have a local Blockbuster that's renting it out, give it a try.