The biggest issue with shadow is that half of the mission objectives are "Kill X amount of Y" It's fucking garbage. 06 might be broken as all hell, but at least it doesn't have that.
I'm not into used copies, but I guess it's an option.
Remember the kill all the fake Chaos mission...holy shit those are awful. Killing 35 annoying foes, with very little feedback or radar is bullshit. And the level wasn't small and everything looked the same.