I just recently played another play-through as a full renegade shep. started ME2 and went to ME3. I was an infiltrator and my sheps name was D-bag Shepard. And he is.
ME2 isn't too brutal, I still got tali and Legion to agree. Miri and Jack went out without a hitch. Although I did give the overlord kid, David to cerberus. And gave TIM the base. But I didn't feel like a raging sociopath in ME2.
Now..... ME3 is a whole other ball game. After playing my shep I felt like I needed to take a shower every-time. Renegade playthrough on ME3 is BRUTAL. Killing Wrex, killing Mordin- that's the worse. Killing Legion, Killing the VS (Udina deserved it). Letting samara blow her brain out, then killing her daughter. yuck. After that I felt like sh!t. ME3 renegade playthrough is full blown Sociopath, it's just awful.
I really don´t know who wrote ME3 but not only Renegade Shepard seems completely crazy also Cerberus went from the shadowy but somehow "good" Organization that tried to defeat the Reapers at all costs to a full blown Sith-empire that had Husk troopers and lures refugees to death camps (Sanctuary) in ME3.
Renegade Commander Shepard acts like he just broke out of a psychiatric clinic right before the game started. I wonder how Tali and the others can work with such a crazy person.