Is there any point? I saw the achievements which say finish Week 2 and Week 3, and I was wondering if there is anything different in each playthrough.

So far, I'm on the end boss on the 2nd playthrough and didn't notice anything different. If there isn't anything new after all three, I wouldn't want to go through the tedious unbalanced game once more. I couldn't care less for the achievements..

btw: This game, no, DEMO is shit.