@hexx462: I'm in the same boat with you, mate. I made it through the first mission, then just completely dropped that whole set of missions and now it's blemish on my nearly fully complete Mass Effect 2 game.
I found the twins to be the biggest pain in the ass. I was level 12, pretty much useless. I realised the only way of getting through it was with plenty of OJ, LMG and a spiked bat/defiler.
The Sgt., wasn't hard, it just pissed me off massively when you're needed to escort the bitch back to the safehouse, AND I DIE. AT THE SAFE HOUSE. AND HAVE TO REDO THE WHOLE FUCKING THING AGAIN. NOT ON.